Method for preventing line bending during metal fill process

ABSTRACT

Provided herein are methods and apparatuses for reducing line bending when depositing a metal such as tungsten, molybdenum, ruthenium, or cobalt into features on substrates by periodically exposing the feature to nitrogen, oxygen, or ammonia during atomic layer deposition, chemical vapor deposition, or sequential chemical vapor deposition to reduce interactions between metal deposited onto sidewalls of a feature. Methods are suitable for deposition into V-shaped features.

INCORPORATION BY REFERENCE

An Application Data Sheet is filed concurrently with this specificationas part of the present application. Each application that the presentapplication claims benefit of or priority to as identified in theconcurrently filed Application Data Sheet is incorporated by referenceherein in its entirety and for all purposes.

BACKGROUND

Deposition of tungsten-containing materials is an integral part of manysemiconductor fabrication processes. These materials may be used forhorizontal interconnects, vias between adjacent metal layers, contactsbetween metal layers and devices on the silicon substrate, and highaspect ratio features. In a conventional tungsten deposition process ona semiconductor substrate, the substrate is heated to a processtemperature in a vacuum chamber, and a very thin portion of tungstenfilm, which serves as a seed or nucleation layer, is deposited.Thereafter, the remainder of the tungsten film (the bulk layer) isdeposited on the nucleation layer by exposing the substrate to tworeactants simultaneously. The bulk layer is generally deposited morerapidly than the nucleation layer. However, as devices shrink and morecomplex patterning schemes are utilized in the industry, deposition ofthin tungsten films becomes a challenge.

SUMMARY

Provided herein are methods and apparatus for depositing metal intofeatures on substrates. One aspect involves a method of filling featureson a substrate to form lines, the method including: (a) providing asubstrate having a plurality of features spaced apart with a pitchbetween adjacent features of about 20 nm and about 40 nm, each featurehaving a feature opening width whereby the width of the feature narrowsfrom the top of the feature to the bottom of the feature; (b) depositinga first amount of tungsten in the plurality of features on thesubstrate; (c) after depositing the first amount of tungsten, exposingthe first amount of tungsten in the plurality of features to nitrogengas; and (d) depositing a second amount of tungsten over the firstamount of tungsten in the plurality of features.

In various embodiments, the nitrogen gas reduces tungsten-tungstenbonding interactions between tungsten formed on sidewalls of eachfeature.

In various embodiments, the width of the bottom of each feature isbetween 0 nm and 90% of the width at the top of the each feature.

The method may also include filling the features with tungsten tothereby form the lines, whereby the total variance of the lines withinthe substrate calculated by σ=(σ₁ ²+σ₂ ²)^(1/2) where σ₁ is variableline-to-line width variance and σ₂ is within-line width variance is lessthan about 5 nm.

In various embodiments, the width at the bottom 50% of the depth of thefeature is between 0 nm and 20 nm.

In various embodiments, the first amount of tungsten is exposed to thenitrogen gas at a substrate temperature less than about 500° C.

In some embodiments, the first amount of tungsten is exposed to thenitrogen gas during the depositing of the second amount of tungsten overthe first amount of tungsten.

In some embodiments, the second amount of tungsten is deposited byalternating pulses of hydrogen and a tungsten-containing precursor. Thefirst amount of tungsten may be exposed to the nitrogen gas during thepulse of hydrogen. In some embodiments, the first amount of tungsten isexposed to the nitrogen gas during the pulse of the tungsten-containingprecursor. In some embodiments, the first amount of tungsten is exposedto argon between the alternating pulses of the hydrogen and thetungsten-containing precursor. The first amount of tungsten may beexposed to the nitrogen when the feature is exposed to the argon betweenthe alternating pulses of the hydrogen and the tungsten-containingprecursor.

Another aspect involves a method filling features on a substrate to formlines including: (a) providing a substrate having a plurality offeatures spaced apart with a pitch between adjacent features of about 20nm and about 40 nm, each feature having a feature opening width wherebythe width of the feature narrows from the top of the feature to thebottom of the feature; (b) depositing a first amount of a metal in theplurality of features on the substrate; (c) after depositing the firstamount of the metal, exposing the first amount of the metal in theplurality of features to an inhibition gas; and (d) depositing a secondamount of the metal over the first amount of the metal in the pluralityof features. The metal may be any one or more of ruthenium, molybdenum,and cobalt. The inhibition gas may be any of nitrogen, oxygen, ammonia,and combinations thereof.

In various embodiments, the inhibition gas reduces metal-metal bondinginteractions between metal formed sidewalls of each feature. In someembodiments, the width of the bottom of each feature is between 0 nm and90% of the width at the top of the each feature. The method may alsoinclude filling the features with the metal to thereby form the lines,wherein the total variance of the lines within the substrate calculatedby σ=(σ₁ ²+σ₂ ²)^(1/2) where σ₁ is variable line-to-line width varianceand σ₂ is within-line width variance is less than about 5 nm. The widthat the bottom 50% of the depth of the feature may be between 0 nm and 20nm.

Another aspect involves an apparatus for processing semiconductorsubstrates, the apparatus having (a) at least one process chamberincluding a pedestal configured to hold a substrate; (b) at least oneoutlet for coupling to a vacuum; (c) one or more process gas inletscoupled to one or more process gas sources; and (d) a controller forcontrolling operations in the apparatus, including machine-readableinstructions for: providing a substrate having a plurality of featuresspaced apart with a pitch between adjacent features of about 20 nm andabout 40 nm, each feature having a feature opening whereby the width ofthe feature narrows from the top of the feature to the bottom of thefeature, introducing a tungsten-containing precursor and a reducingagent to deposit a first amount of tungsten in the plurality of featureson the substrate; after depositing the first amount of tungsten,introducing a nitrogen gas to the first amount of tungsten in theplurality of features, and introducing the tungsten-containing precursorand the reducing agent to deposit a second amount of tungsten over thefirst amount of tungsten in the plurality of features.

These and other aspects are described further below with reference tothe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of example films on a substrate.

FIG. 2A depicts a schematic illustration of an example of a dynamicrandom access memory (DRAM) architecture including a buried wordline(bWL) in a silicon substrate.

FIG. 2B depicts a schematic illustration of line bending.

FIG. 2C depicts a schematic illustration of a zipping phenomenon.

FIG. 2D is a graph showing the interatomic force as a function oftungsten-tungsten bond radius.

FIGS. 3A-3I are schematic examples of various structures in which ametal such as tungsten may be deposited in accordance with certaindisclosed embodiments.

FIGS. 4A-4D are process flow diagrams depicting operations for methodsperformed in accordance with certain disclosed embodiments.

FIGS. 5A-5J and 6 are schematic diagrams of an example of a mechanismfor depositing films in accordance with certain disclosed embodiments.

FIGS. 7-11 are timing sequence diagrams showing example cycles invarious methods in accordance with certain disclosed embodiments.

FIG. 12 is a schematic diagram of an example process tool for performingdisclosed embodiments.

FIG. 13 is a schematic diagram of an example station for performingdisclosed embodiments.

FIG. 14 depicts various timing sequence diagrams.

FIGS. 15, 16, 17, 18A-18B, and 19A-19B are plots of experimentalresults.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the presented embodiments. Thedisclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with specific embodiments, it will be understood that it isnot intended to limit the disclosed embodiments.

Metal fill, such as tungsten (W) fill, of features is often used insemiconductor device fabrication to form electrical contacts. There arevarious challenges in tungsten fill as devices scale to smallertechnology nodes and more complex patterning structures are used. Onechallenge is reducing the fluorine concentration or content in thedeposited tungsten film. As compared to larger features, a smallerfeature having the same fluorine concentration in the tungsten film as alarger feature affects the performance of the device more substantially.For example, the smaller the feature, the thinner the films aredeposited. As a result, fluorine in the deposited tungsten film is morelikely to diffuse through the thinner films, thereby potentially causingdevice failure.

One method of preventing fluorine diffusion includes depositing one ormore barrier layers prior to depositing tungsten to prevent fluorinefrom diffusing from tungsten to other layers of the substrate such as anoxide layer. For example, FIG. 1 shows an example stack of layersdeposited on a substrate 190. Substrate 190 includes a silicon layer192, an oxide layer 194 (e.g., titanium oxide (TiOx), tetraethylorthosilicate (TEOS) oxide, etc.), a barrier layer 196 (e.g., titaniumnitride (TiN)), a tungsten nucleation layer 198, and a bulk tungstenlayer 199. Barrier layer 196 is deposited to prevent fluorine diffusionfrom the bulk tungsten layer 199 and the tungsten nucleation layer 198to the oxide layer. However, as devices shrink, barrier layers becomethinner, and fluorine may still diffuse from the deposited tungstenlayers. Although chemical vapor deposition of bulk tungsten performed ata higher temperature results in lower fluorine content, such films havepoor step coverage.

Another challenge is reducing resistance in the deposited tungstenfilms. Thinner films tend to have higher resistance than thicker films.As features become smaller, the tungsten contact or line resistanceincreases due to scattering effects in the thinner tungsten films. Lowresistivity tungsten films minimize power losses and overheating inintegrated circuit designs. Tungsten nucleation layers typically havehigher electrical resistivities than the overlying bulk layers. Barrierlayers deposited in contacts, vias, and other features, may also havehigh resistivities. Further, thin barrier and tungsten nucleation filmsoccupy a larger percentage of smaller features, increasing the overallresistance in the feature. Resistivity of a tungsten film depends on thethickness of the film deposited, such that resistivity increases asthickness decreases due to boundary effects.

Another challenge is reducing stress on deposited films. Thinnertungsten films tend to have increased tensile stress. Conventionaltechniques for depositing bulk tungsten films by chemical vapordeposition have a tensile stress greater than 2.5 GPa for a 200 Å film.High thermal tensile stress causes the substrate to curl, which makessubsequent processing difficult. For example, subsequent processes mayinclude chemical mechanical planarization, deposition of materials,and/or clamping of the substrate to a substrate holder to performprocesses in a chamber. However, these processes often rely on thesubstrate being flat, and a curled substrate results in nonuniformprocessing or inability to process the substrate. Although there areexisting methods for reducing stress in films of other materials such asannealing, tungsten does not have the surface mobility to allow grainsto be moved or altered once it is deposited due to its high meltingpoint.

Another challenge is reducing line bending, a phenomenon found in, forexample, substrates having multiple features with narrow pitch, or insubstrates multiple high aspect ratio features adjacent to one another.Line bending in dynamic random-access memory (DRAM) buried wordlinestructures (bWL) during tungsten fill is believed to be caused by grainboundary merging (which may be referred to as a “zipping mechanism”).When the grain boundaries are formed, the tungsten-tungsten bondingbetween adjacent tungsten surfaces (such as the growing tungsten film onsidewalls of a feature) causes strain that leads to bending of thesilicon fins (lines) separating the bWL. Conventional ALD and chemicalvapor deposition (CVD) tungsten fill techniques result in severe bendingof the bWL structures. This line bending will cause tungsten recessnon-uniformity and contact landing issues in downstream processes, whichresults in DRAM yield loss.

Conventional 2-D growth may exhibit low stress, low fluorine, and lowresistivity tungsten films by ALD but only on surfaces that allow forsuch growth. As devices shrink and features are narrower, there may be azipping mechanism, which can cause tensile stress, high incorporation offluorine, and impact on resistivity resulting in rough morphology.

Particular embodiments relate to methods and related apparatus forformation of tungsten wordlines in memory devices. FIG. 2A depicts aschematic example of a DRAM architecture including a buried wordline(bWL) 11 in a silicon substrate 9. The bWL 11 is formed in a trenchetched in the silicon substrate 9. The bWL 11 is tungsten deposited inthe silicon substrate 9 and is capped by SiN passivation 5. Lining thetrench is a conformal barrier layer 12 and an insulating layer 13 thatis disposed between the conformal barrier layer 12 and the siliconsubstrate 9. In the example of FIG. 2A, the insulating layer 13 may be agate oxide layer, formed from a material such as a silicon oxide.Examples of conformal barrier layers include titanium nitride (TiN) andtungsten-containing barrier layers. Tungsten-containing conformalbarrier layers are described in U.S. Patent Application Publication No.2016/0233220 (Ser. No. 15/040,561), filed Feb. 10, 2016, titled“TUNGSTEN FOR WORDLINE APPLICATIONS,” which is incorporated by referenceherein.

Conventional deposition processes for DRAM bWL trenches tend to distortthe trenches such that the final trench width and resistance Rs aresignificantly non-uniform. FIG. 2B shows an unfilled (201) and filled(205) narrow asymmetric trench structure typical of DRAM bWL. As shown,multiple features are depicted on a substrate. These features may bespaced apart where adjacent features have a pitch between about 20 nmand about 40 nm. The pitch is defined as the distance between the middleaxis of one feature to the middle axis of an adjacent feature. Theunfilled features are generally V-shaped as shown in feature 203, havingsloped sidewalls where the width of the feature narrows from the top ofthe feature to the bottom of the feature. The features widen from thefeature bottom 213 b to the feature top 213 a. After tungsten fill,severe line bending is observed in substrate 205. Without being bound bya particular theory, it is believed that a cohesive force betweenopposing surfaces of a trench pulls the trench sides together asdepicted by arrows 207. This phenomena is illustrated in FIG. 2C, andmay be characterized as “zipping up” the feature. As the feature 203 isfilled, more force is exerted from a center axis 299 of the feature 203,causing line bending. Deposited tungsten 243 a and 243 b on sidewalls offeature 203 thereby interact in close proximity, where tungsten-tungstenbond radius r is small, thereby causing cohesive interatomic forcesbetween the smooth growing surfaces of tungsten and pulling thesidewalls together, thereby causing line bending. FIG. 2D illustratesthe interatomic force as a function of tungsten-tungsten bond radius, r.As can be seen, a cohesive force exists at certain values of r.

Until recently, the bWL bending was believed to be caused by theintrinsic tungsten film stress during the fill. However, as noted above,the low stress tungsten films deposited by conventional ALD processescan cause severe line bending during the fill. An alternate explanationbased on grain boundary zipping mechanism was proposed to explain theline bending.

Described herein are methods of filling features with metal and relatedsystems and apparatuses for using an inhibition gas to reduce formationof metal-metal bonding and thereby reduce line bending. Inhibition gasesinclude nitrogen, oxygen, ammonia, and combinations thereof, dependingon the metal to be deposited and the conditions and chemistries used fordeposition of the metal to be deposited. Various embodiments involveexposing the feature with partially filled metal to the inhibition gaswithout a plasma to reduce formation of metal-metal bonding in thefeature. Certain disclosed embodiments are particularly suitable forfilling V-shaped features as described herein.

Certain disclosed embodiments utilize the addition of nitrogen gas (N₂)during tungsten fill to disrupt the formation of tungsten-tungstenbonding, which reduces the strain in the bWL structure. Nitrogenaddition can be done in a pulsed form (e.g., during a H₂ co-reactantpulse or purge pulse in a cyclic deposition technique such as atomiclayer deposition (ALD), or sequential chemical vapor deposition (CVD),which are further described below) or in a continuous form during anysuitable deposition technique, such as during an ALD cycle. Althoughvarious examples and embodiments herein are described with respect totungsten, it will be understood that disclosed embodiments are suitablefor depositing a variety of metals, including but not limited toruthenium, molybdenum, cobalt, and more. Examples of applicationsinclude logic and memory contact fill, DRAM buried wordline fill,vertically integrated memory gate/wordline fill, and 3-D integrationwith through-silicon vias (TSVs). The methods described herein can beused to fill vertical features, such as in tungsten vias, and horizontalfeatures, such as 3D-NAND wordlines. The methods may be used forconformal and bottom-up or inside-out fill.

Adding nitrogen during CVD and a pulsed nucleation layer (PNL) processis described in U.S. Pat. No. 8,551,885, filed on Aug. 29, 2008 andissued on Oct. 8, 2013, entitled “METHOD FOR REDUCING TUNGSTEN ROUGHNESSAND IMPROVING REFLECTIVITY” which is herein incorporated by reference inits entirety. As described there, nitrogen may be added to control thefilm roughness and improve tungsten fill.

Described herein are methods of preventing line bending by the additionof an inhibition gas such as nitrogen. Nitrogen addition is especiallyeffective during ALD tungsten fill and sequential CVD tungsten fillsince the film growth via a 2-D mechanism enhances the grain zippingmechanism.

Disclosed embodiments may block the surface of the growing tungsten filmduring the bWL fill process using nitrogen molecules. The W—N₂ bondingweakens the W—W interaction when the adjacent surfaces of the growingfilm merge, thus reducing the strain that would otherwise cause siliconline deflection. The process conditions can be modulated to minimize thenitrogen (N) incorporation into the film to maintain low resistivity ofthe tungsten fill.

Nitrogen is used in combination with a tungsten-containing precursor WF₆to allow adsorbed N₂ molecules to disrupt W—W bonding interactionsduring the grain boundary merging such that the interactions will notcause increase stress on the film. The H₂ dose used to convert thetungsten-containing precursor to tungsten reacts to generate HF, whichis desorbed and removed from the chamber. Weakly bonded N₂ molecules mayremain on the tungsten surface in subsequent cycles of sequential CVDbut may generally be used to reduce W—W bonding interactions at thegrain boundary to promote gap fill progression without stress on thedeposited tungsten film.

Disclosed embodiments include methods of depositing tungsten filmshaving a low fluorine concentration using a sequential CVD process incombination with exposure to an inhibition gas such as nitrogen toreduce line bending. The deposited films may also have low stress.Certain methods involve introducing hydrogen and a tungsten-containingprecursor such as tungsten hexafluoride in cycles. Disclosed embodimentsmay be integrated with other tungsten deposition processes to deposit alow stress tungsten film having substantially lower fluorine contentthan films deposited by conventional CVD. For example, sequential CVDprocesses may be integrated with nucleation layer deposition at lowpressure, fluorine-free tungsten layer deposition, and/or non-sequentialCVD processes. Disclosed embodiments have a wide variety ofapplications. Methods may be used to deposit tungsten into features withhigh step coverage, and may also be used to deposit tungsten into 3DNAND structures, including those with deep trenches. Further, themethods may be implemented for architectures that may otherwise besusceptible to line bending by the addition of nitrogen during theprocess.

Sequential CVD processes are distinguished from non-sequential CVD,pulsed CVD, atomic layer deposition (ALD), and nucleation layerdeposition. Non-sequential CVD processes involve simultaneous exposureof two reactants, such that both reactants are flowed at the same timeduring deposition. For example, bulk tungsten may be deposited byexposing a substrate to hydrogen (H₂) and tungsten hexafluoride (WF₆) atthe same time for a duration sufficient to fill features. Hydrogen andWF₆ react during the exposure to deposit tungsten into the features. Inpulsed CVD processes, one reactant is continuously flowed while theother reactant is pulsed, but the substrate is exposed to both reactantsduring deposition to deposit material during each pulse. For example, asubstrate may be exposed to a continuous flow of H₂ while WF₆ is pulsed,and WF₆ and H₂ react during the pulse to deposit tungsten.

In contrast, sequential CVD processes implement separate exposures toeach reactant such that the reactants are not flowed into the chamber atthe same time during deposition. Rather, each reactant flow isintroduced to a chamber housing the substrate in temporally separatedpulses in sequence, repeated one or more times in cycles. Generally, acycle is the minimum set of operations used to perform a surfacedeposition reaction one time. The result of one cycle is the productionof at least a partial film layer on a substrate surface. Cycles ofsequential CVD are described in further detail below.

ALD and nucleation layer deposition also involve exposing the substrateto two reactants in temporally separated pulses in cycles. For example,in an ALD cycle, a first reactant is flowed into a chamber, the chamberis purged, a second reactant is flowed into the chamber, and the chamberis again purged. Such cycles are typically repeated to build filmthickness. In conventional ALD and nucleation layer deposition cycles,the first reactant flow constitutes a first “dose” in a self-limitingreaction. For example, a substrate includes a limited number of activesites whereby a first reactant is adsorbed onto the active sites on thesubstrate and saturates the surface, and a second reactant reacts withthe adsorbed layer to deposit material layer by layer in cycles.

However, in sequential CVD, reactants do not necessarily adsorb ontoactive sites on the substrate and in some embodiments, the reaction maynot be self-limiting. For example, reactants used in sequential CVD mayhave a low adsorption rate. Moreover, reactants on the surface of thesubstrate may not necessarily react with a second reactant when thesecond reactant is introduced. Rather, in some embodiments of sequentialCVD, some reactants on the substrate remain unreacted during the cycle,and are not reacted until a subsequent cycle. Some reactants may notreact due to stoichiometric properties, steric hindrance, or othereffects.

Methods described herein are performed on a substrate that may be housedin a chamber. The substrate may be a silicon wafer, e.g., a 200-mmwafer, a 300-mm wafer, or a 450-mm wafer, including wafers having one ormore layers of material, such as dielectric, conducting, orsemi-conducting material deposited thereon. Substrates have featuressuch as via or contact holes, which may be characterized by one or moreof V-shaped sidewalls, narrow and/or re-entrant openings, constrictionswithin the feature, and high aspect ratios. A feature may be formed inone or more of the above described layers. For example, the feature maybe formed at least partially in a dielectric layer. In some embodiments,a feature may have an aspect ratio of at least about 2:1, at least about4:1, at least about 6:1, at least about 10:1, or higher. One example ofa feature is a hole or via in a semiconductor substrate or a layer onthe substrate. Features may be spaced apart on the substrate by a pitchbetween adjacent features of about 20 nm to about 40 nm.

FIGS. 3A-3G are schematic examples of various structures in whichtungsten may be deposited in accordance with disclosed embodiments. FIG.3A shows an example of a cross-sectional depiction of a vertical feature301 to be filled with tungsten. The feature 301 can include a featurehole 305 in a substrate 303. The hole 305 or other feature may have adimension near the opening, e.g., an opening diameter or line width ofbetween about 10 nm to 500 nm, for example between about 25 nm and about300 nm. The feature hole 305 can be referred to as an unfilled featureor simply a feature. The feature 301, and any feature, may becharacterized in part by an axis 318 that extends through the length ofthe feature through the center of the hole 305, with vertically-orientedfeatures having vertical axes and horizontally-oriented features havinghorizontal axes.

In some embodiments, features are trenches in a 3D NAND structure. Forexample, a substrate may include a wordline structure having at least 60lines, with 18 to 48 layers, or hundreds of layers, with trenches atleast 200 Å deep or many microns dee. Another example is a trench in asubstrate or layer. Features may be of any depth. In variousembodiments, the feature may have an under-layer, such as a barrierlayer or adhesion layer. Non-limiting examples of under-layers includedielectric layers and conducting layers, e.g., silicon oxides, siliconnitrides, silicon carbides, metal oxides, metal nitrides, metalcarbides, and metal layers.

FIG. 3B shows an example of a feature 301 that has a re-entrant profile.A re-entrant profile is a profile that narrows from a bottom, closedend, or interior of the feature to the feature opening. According tovarious implementations, the profile may narrow gradually and/or includean overhang at the feature opening. FIG. 3B shows an example of thelatter, with an under-layer 313 lining the sidewall or interior surfacesof the feature hole 305 of feature 301. The under-layer 313 can be forexample, a diffusion barrier layer, an adhesion layer, a nucleationlayer, a combination of thereof, or any other applicable material.Non-limiting examples of under-layers can include dielectric layers andconducting layers, e.g., silicon oxides, silicon nitrides, siliconcarbides, metal oxides, metal nitrides, metal carbides, and metallayers. In particular implementations an under-layer can be one or moreof Ti, TiN, WN, TiAl, and W. The under-layer 313 forms an overhang 315such that the under-layer 313 is thicker near the opening of the feature301 than inside the feature 301.

In some implementations, features having one or more constrictionswithin the feature may be filled. FIG. 3C shows examples of views ofvarious filled features having constrictions. Each of the examples (a),(b) and (c) in FIG. 3C includes a constriction 309 at a midpoint withinthe feature. The constriction 309 can be, for example, between about 15nm-20 nm wide. Constrictions can cause pinch off during deposition oftungsten in the feature using conventional techniques, with depositedtungsten blocking further deposition past the constriction before thatportion of the feature is filled, resulting in voids in the feature.Example (b) further includes a liner/barrier overhang 315 at the featureopening. Such an overhang could also be a potential pinch-off point.Example (c) includes a constriction 312 further away from the fieldregion than the overhang 315 in example (b).

Horizontal features, such as in 3-D memory structures, can also befilled. FIG. 3D shows an example of a horizontal feature 350 thatincludes a constriction 351. For example, horizontal feature 350 may bea word line in a 3D NAND structure.

In some implementations, the constrictions can be due to the presence ofpillars in a 3D NAND or other structure. FIG. 3E, for example, shows aplan view of pillars 325 in a 3D NAND or vertically integrated memory(VIM) structure 348, with FIG. 3F showing a simplified schematic of across-sectional depiction of the pillars 325. Arrows in FIG. 3Erepresent deposition material; as pillars 325 are disposed between anarea 327 and a gas inlet or other deposition source, adjacent pillarscan result in constrictions 351 that present challenges in void freefill of an area 327.

The structure 348 can be formed, for example, by depositing a stack ofalternating interlayer dielectric layers 329 and sacrificial layers (notshown) on a substrate 300 and selectively etching the sacrificiallayers. The interlayer dielectric layers may be, for example, siliconoxide and/or silicon nitride layers, with the sacrificial layers amaterial selectively etchable with an etchant. This may be followed byetching and deposition processes to form pillars 325, which can includechannel regions of the completed memory device.

The main surface of substrate 300 can extend in the x and y directions,with pillars 325 oriented in the z-direction. In the example of FIGS. 3Eand 3F, pillars 325 are arranged in an offset fashion, such that pillars325 that are immediately adjacent in the x-direction are offset witheach other in the y-direction and vice versa. According to variousimplementations, the pillars (and corresponding constrictions formed byadjacent pillars) may be arranged in any number of manners. Moreover,the pillars 325 may be any shape including circular, square, etc.Pillars 325 can include an annular semi-conducting material, or circular(or square) semi-conducting material. A gate dielectric may surround thesemi-conducting material. The area between each interlayer dielectriclayer 329 can be filled with tungsten; thus structure 348 has aplurality of stacked horizontally-oriented features that extend in the xand/or y directions to be filled.

FIG. 3G provides another example of a view of a horizontal feature, forexample, of a 3D NAND or other structure including pillar constrictions351. The example in FIG. 3G is open-ended, with material to be depositedable to enter horizontally from two sides as indicated by the arrows.(It should be noted that example in FIG. 3G can be seen as a 2-Drendering 3-D features of the structure, with the FIG. 3G being across-sectional depiction of an area to be filled and pillarconstrictions shown in the figure representing constrictions that wouldbe seen in a plan rather than cross-sectional view.) In someimplementations, 3-D structures can be characterized with the area to befilled extending along two or three dimensions (e.g., in the x and y orx, y and z-directions in the example of FIG. 3F), and can present morechallenges for fill than filling holes or trenches that extend along oneor two dimensions. For example, controlling fill of a 3-D structure canbe challenging as deposition gasses may enter a feature from multipledimensions.

FIG. 3H provides an example of a cross-sectional view of a V-shapedfeature. FIG. 3H includes feature 301 to be filled with tungsten,including a feature hole 305 in a substrate 303. The hole has adimension near the opening (e.g., an opening diameter or a line width w,which may be between about 10 nm and about 20 nm, or about 15 nm). Thewidth is measured by the distance between sidewalls of a feature. Thewidth may vary from the top of the feature at the feature opening (theopening diameter or line width w) to the bottom of the feature. Thefeature hole 305 is characterized in part by an axis 318. The V-shapedfeature 301 includes a depth 350 which may be between about 80 nm andabout 120 nm, or about 100 nm. In various embodiments, the sidewallsmeet at a point 395 at the bottom of the feature or in some embodiments,the bottom of the feature plateaus to a flat bottom surface, which mayhave a distance from one sidewall to the other of between about 0.1w andabout 0.9w, or as a percentage of line width w at the opening of about10% of the width w to about 90% of the width w. Features may have anaspect ratio of between 2:1 and about 10:1, or between about 6:1 andabout 8:1, or about 6:1, or about 8:1. The pitch of the lines may bebetween about 20 nm and about 40 nm. The bottom of the feature, which ischaracterized as the region in the bottom 50% to 70% of the depth of thefeature, may have a width between sidewalls of between 0 nm and about 20nm.

FIG. 3I provides another example of a cross-sectional view of a V-shapedfeature. The V-shaped feature as described herein refers to featureshaving narrowing width from the top field level of the substrate to thebottom of the feature. FIG. 3I includes feature 301 to be filled with ametal such as tungsten, including a feature hole 305 in a substrate 303.The hole has a dimension near the opening (e.g., an opening diameter ora line width w, which may be between about 10 nm and about 20 nm, orabout 15 nm). The bottom of the feature 396 has a width narrower thanthat of w. For example, the bottom of the feature 396 may have a widthbetween 1% and 90% of the width w, or between 1% and 50%, or between 10%and 20% of the width w.

Multiple V-shaped features are present on a substrate in variousdisclosed embodiments, such as shown in FIG. 2B. Multiple features on asubstrate are defined as adjacent features having a distance no largerthan between 20 nm and 40 nm of each other. In various embodiments, suchmultiple features includes all V-shaped features, which may have a shapesuch as depicted in FIG. 3H or 3I.

Examples of feature fill for horizontally-oriented andvertically-oriented features are described below. It should be notedthat the examples applicable to both horizontally-oriented orvertically-oriented features. Moreover, it should also be noted that inthe description below, the term “lateral” may be used to refer to adirection generally orthogonal to the feature axis and the term“vertical” to refer to a direction generally along the feature axis.

While the description below focuses on tungsten feature fill, aspects ofthe disclosure may also be implemented in filling features with othermaterials. For example, feature fill using one or more techniquesdescribed herein may be used to fill features with other materialsincluding other tungsten-containing materials (e.g., tungsten nitride(WN) and tungsten carbide (WC)), titanium-containing materials (e.g.,titanium (Ti), titanium nitride (TiN), titanium silicide (TiSi),titanium carbide (TiC) and titanium aluminide (TiAl)),tantalum-containing materials (e.g., tantalum (Ta), and tantalum nitride(TaN)), and nickel-containing materials (e.g., nickel (Ni) and nickelsilicide (NiSi). Further, some of the methods and apparatus disclosedherein are not limited to feature fill, but can be used to deposittungsten on any appropriate surface including forming blanket films onplanar surfaces.

FIG. 4A provides a process flow diagram for a method performed inaccordance with certain disclosed embodiments. Operations 402-410 ofFIG. 4A are performed to deposit a tungsten nucleation layer by ALD.Operation 495 involves exposing the substrate to nitrogen. Operations402, 404, 406, 408, 495, and 410 are performed to deposit a tungstennucleation layer in accordance with various embodiments. In variousembodiments described herein, operations 402-410 are performed at lowerpressure than operation 480. For example, operations 402-410 may beperformed at a low pressure less than about 10 Torr. In some examples,operations 402-410 are performed at a pressure of about 10 Torr, or apressure of about 3 Torr. Without being bound by a particular theory, itis believed that performing operations 402-410 at a low pressure reducesfluorine concentration in the deposited tungsten film due to a lowerpartial pressure of a fluorine-containing precursor in the chamber whenthe film is deposited, such that less fluorine is incorporated into thefilm. Examples of processes for depositing a tungsten nucleation layerat low pressure to achieve low fluorine concentration in depositedtungsten are further described in U.S. patent application Ser. No.14/723,275 (Attorney Docket No. LAMRP183/3623-1US) filed on May 27,2015.

In operation 402, the substrate is exposed to a tungsten-containingprecursor such as WF₆. For purposes of the description herein, althoughWF₆ is used as an example of a tungsten-containing precursor, it shouldbe understood that other tungsten-containing precursors may be suitablefor performing disclosed embodiments. For example, a metal-organictungsten-containing precursor may be used. Organo-metallic precursorsand precursors that are free of fluorine, such as MDNOW(methylcyclopentadienyl-dicarbonylnitrosyl-tungsten) and EDNOW(ethylcyclopentadienyl-dicarbonylnitrosyl-tungsten) may also be used.Chlorine-containing tungsten precursors (WCl_(x)) such as tungstenpentachloride (WCl₅) and tungsten hexachloride (WCl₆) may be used.

In this example, the tungsten-containing precursor may include acombination of these compounds. In some embodiments, a carrier gas, suchas nitrogen (N₂), argon (Ar), helium (He), or other inert gases, may beflowed during operation 402. The carrier gas with thetungsten-containing precursor may be diverted before delivery to thesubstrate in some embodiments.

While tungsten is described herein, it will be understood that in someembodiments, another metal may be deposited instead of tungsten, byusing a suitable metal-containing precursor. For example, for depositionof molybdenum into features, a molybdenum-containing precursor such asmolybdenum tetrachloride (MoCl₄) may be used.

Operation 402 may be performed for any suitable duration and at anysuitable temperature. In some examples, operation 402 may be performedfor a duration between about 0.25 seconds and about 30 seconds, about0.25 seconds to about 5 seconds, or about 0.5 seconds to about 3seconds. This operation may be performed in some embodiments for aduration sufficient to saturate the active sites on the surface of thesubstrate.

In operation 404, the chamber is optionally purged to remove excess WF₆that did not adsorb to the surface of the substrate. A purge may beconducted by flowing an inert gas at a fixed pressure thereby reducingthe pressure of the chamber and re-pressurizing the chamber beforeinitiating another gas exposure.

In operation 406, the substrate is exposed to a reducing agent todeposit a tungsten nucleation layer. The reducing agent may be a borane,silane, or germane. Example boranes include borane (BH₃), diborane(B₂H₆), triborane, alkyl boranes, aminoboranes, carboranes, andhaloborane. Example silanes include silane (SiH₄), disilane (Si₂H₆),trisilane (Si₃H₈), alkyl silanes, aminosilanes, carbosilanes, andhalosilane. Germanes include Ge_(n)H_(n+4), Ge_(n)H_(n+6),Ge_(n)H_(n+8), and Ge_(n)H_(m), where n is an integer from 1 to 10, andn is a different integer than m. Other germanes may also be used, e.g.,alkyl germanes, aminogermanes, carbogermanes, and halogermanes. Ingeneral, halogermanes may not have significant reducing potential butthere may be process conditions and tungsten-containing precursorssuitable for film formation using halogermanes.

Operation 406 may be performed for any suitable duration. In someexamples, Example durations include between about 0.25 seconds and about30 seconds, about 0.25 seconds to about 5 seconds, or about 0.5 secondsto about 3 seconds. In some embodiments, this operation may besufficient to react with the adsorbed layer of WF₆ on the surface of thesubstrate. Operation 406 may be performed for a duration outside ofthese example ranges. In some embodiments, a carrier gas may be used,such as, for example, argon (Ar), helium (He), or nitrogen (N₂).

After operation 406, there may be an optional purge step to purge excessreducing agent still in gas phase that did not react with WF₆ on thesurface of the feature. A purge may be conducted by flowing an inert gasat a fixed pressure thereby reducing the pressure of the chamber andre-pressurizing the chamber before initiating another gas exposure.

In operation 408, the chamber is purged to remove any reactionby-products. The chamber may be purged by introducing a purge gas, suchas an inert gas, or may be performed by expunging the chamber. Exampleinert gases include but are not limited to hydrogen, argon, and helium.

In operation 495, the substrate is exposed to nitrogen. Nitrogenpassivates the substrate, which can thereby reduce tungsten-tungstenbonding from the sidewalls of features on the substrate. In someembodiments, an inert gas may be flowed with the nitrogen to thesubstrate. Example inert gases include argon, helium, and hydrogen. Inembodiments where a combination of nitrogen and hydrogen are introduced,the mixture of nitrogen and hydrogen may include at least about 10%nitrogen, or between about 1c % to about 100% nitrogen gas.

Operation 495 is performed at a temperature less than about 500° C. orless than about 450° C. At temperatures above 500° C., undesirednitrogen atoms may be incorporated into the tungsten film in thefeature. Operation 495 may be performed at the same pressure as thepressure used in operations 402-408. In some embodiments, operation 495is performed at a different pressure than the pressure used inoperations 402-408 and the pressure is modulated between the twopressures for each cycle.

In various embodiments, other inhibition gases may be used instead ofnitrogen. In various embodiments, oxygen may be used in lieu of nitrogenin some embodiments. In some embodiments, the inhibition gas may benitrogen, oxygen, ammonia, or combinations thereof, depending on themetal to be deposited and the metal-containing precursor used fordeposition. For example, in some embodiments, ammonia (NH₃) may beflowed instead of or in addition to nitrogen to prevent metal-metalbonding from deposited material on the sidewalls of the substrate. Ifammonia is used, the tungsten-containing precursor is not co-flowed withammonia so as to prevent reaction between the tungsten-containingprecursor and ammonia. For example, as described further below, in someembodiments nitrogen is introduced continuously or in pulses. Wheretungsten hexafluoride is used as the tungsten-containing precursor,ammonia is introduced only in pulses, or only when the tungstenhexafluoride is not introduced to the substrate.

In operation 410, it is determined whether the tungsten nucleation layerhas been deposited to an adequate thickness. If not, operations 402-408are repeated until a desired thickness of a tungsten nucleation layer isdeposited on the surface of the feature. Additionally, operation 495 maybe performed in every repeated cycle, or every 2 cycles, or every 3cycles, or every 4 cycles, or less frequently. Each repetition ofoperations 402-408 may be referred to as an ALD “cycle.” In someembodiments, the order of operations 402 and 406 may be reversed, suchthat reducing agent is introduced first.

After the tungsten nucleation layer is deposited to an adequatethickness, the substrate may be exposed to nitrogen (or oxygen or anitrogen-containing gas such as ammonia) in operation 499. Followingexposure to nitrogen in operation 499, in operation 480, bulk tungstenis deposited by sequential CVD. While sequential CVD is describedherein, in some embodiments, bulk tungsten may be deposited by anysuitable method, such as CVD or ALD. In various embodiments, operation480 may be performed at a pressure greater than the pressure duringoperations 402-410. For example, operation 480 may be performed at apressure greater than or equal to about 10 Torr, for example about 10Torr, or about 40 Torr.

FIG. 4B provides a process flow diagram for operations that may beperformed during operation 480 after exposure to nitrogen in operation499. It will be understood that operation 499 may be performedcontinuously such that nitrogen gas is flowed continuously during bulkdeposition of tungsten by sequential CVD, or in some embodiments may bepulsed periodically, such as pulsed only during reducing agent exposure,or pulsed only during a purge gas operation, or pulsed only during onepurge gas operation, or pulsed only during a tungsten-containingprecursor dose, or pulsed during one or more of the above operations.Pulsing may occur during every cycle, or every 2 cycles, or every 3cycles, or every 4 cycles, or less frequently as desired. A combinationof continuous and pulsed exposures may also be used in some embodiments.Further, as described above, where ammonia is used to mitigate reactionsbetween tungsten deposited on opposite sidewalls of a feature, ammoniais not introduced in continuous or pulsed doses duringtungsten-containing precursor exposure, such as during exposure totungsten hexafluoride.

Note that operations of FIG. 4B may be performed without performingoperations of FIG. 4A. In FIG. 4B, in operation 482, the substrate isexposed to a reducing agent, such as H₂. This operation may be referredto as a “pulse” or a “dose,” which may be used interchangeably herein.In embodiments described herein, H₂ is provided as an example reducingagent, but it will be understood that other reducing agents, includingsilanes, boranes, germanes, phosphines, hydrogen-containing gases, andcombinations thereof, may be used. Unlike non-sequential CVD, H₂ ispulsed without flowing another reactant. In some embodiments, a carriergas may be flowed. The carrier gas may be any of those described abovewith respect to operation 404 in FIG. 4A, such as argon or helium.Operation 482 may be performed for any suitable duration. In someexamples, Example durations include between about 0.25 seconds and about30 seconds, about 0.25 seconds to about 5 seconds, or about 0.5 secondsto about 3 seconds.

Returning to FIG. 4B, in operation 484, the chamber is purged. In someembodiments, purging is optional. This purge operation may remove excessH₂ that remained in gas phase. A purge is conducted by flowing an inertgas at a fixed pressure thereby reducing the pressure of the chamber andre-pressurizing the chamber before initiating another gas exposure. Thechamber may be purged for any suitable duration, for example, for aduration between about 0.1 seconds and about 3 seconds.

Returning to FIG. 4B, in operation 486, the substrate is exposed to atungsten-containing precursor (e.g., WF₆) to form a sub-monolayer offilm on the substrate. Other tungsten-containing precursors may be usedin some embodiments. Although WF₆ is used as an example of atungsten-containing precursor, it should be understood that othertungsten-containing precursors may be suitable for performing disclosedembodiments. For example, a metal-organic tungsten-containing precursormay be used. Organo-metallic precursors and precursors that are free offluorine, such as MDNOW(methylcyclopentadienyl-dicarbonylnitrosyl-tungsten) and EDNOW(ethylcyclopentadienyl-dicarbonylnitrosyl-tungsten) may also be used.Chlorine-containing tungsten precursors (WCl_(x)) such as tungstenpentachloride (WCl₅) and tungsten hexachloride (WCl₆) may be used.

In this example, the tungsten-containing precursor may include acombination of these compounds. In some embodiments, a carrier gas, suchas nitrogen (N₂), argon (Ar), helium (He), or other inert gases, may beflowed. The carrier gas may be diverted before delivery of thetungsten-containing precursor to the substrate in some embodiments.

While tungsten is described herein, it will be understood that in someembodiments, another metal may be deposited instead of tungsten, byusing a suitable metal-containing precursor. For example, for depositionof molybdenum into features, a molybdenum-containing precursor such asmolybdenum tetrachloride (MoCl₄) may be used.

For purposes of this example, WF₆ is used. In various embodiments, WF₆is flowed to the chamber during this operation for a duration betweenabout 0.1 seconds and about 3 seconds, or about 0.5 seconds. In someembodiments, WF₆ may be diverted to fill the gas line and line changebefore dosing. In some embodiments, WF₆ is flowed to the chamber butdoes not fully react with all H₂ molecules on the surface of thesubstrate.

During operation 486 of FIG. 4B, some WF₆ may react with H₂ thatremained on the surface from the prior dose. During operation 486 ofFIG. 4B, some WF₆ may not fully react with H₂ that remained on thesurface from the prior dose. During operation 486 of FIG. 4B, some WF₆may not react with H₂ at all and may instead be physisorbed onto thesurface of the substrate where no H₂ physisorbed or remained on thesubstrate surface. In some embodiments, WF₆ may remain on the substratesurface but may not be physisorbed or chemisorbed to the surface. Suchexamples are described below with respect to FIGS. 5A-5J in the examplemechanism drawings.

Operation 486 of FIG. 4B may thereby form a sub-monolayer of tungsten inmany embodiments. For example, a sub-monolayer having a thickness ofabout 0.3 Å may be deposited after performing operations 482-486.

In some embodiments, operations 486 and 482 may be reversed such thatoperation 486 is performed before 482. In some embodiments, operation482 may be performed before operation 486.

In operation 488 of FIG. 4B, the chamber is purged to remove reactedbyproducts and WF₆ in gas phase from the chamber. In some embodiments, apurge duration that is too short in operation 488 may increasenon-sequential CVD reaction characteristics such that a higher stressfilm will be deposited. In some embodiments, the purge duration isbetween about 0.1 seconds and about 2 seconds and may prevent removingall of the WF₆ from the substrate surface due to the low adsorption rateof WF₆ to a surface of tungsten. In some embodiments, purge duration isbetween about 0.1 seconds and about 15 seconds, such as about 7 seconds.For example, for fabrication of a 3D NAND structure, the chamber may bepurged for about 7 seconds during operation 288. The purge durationdepends on the substrate and stress.

In operation 490 of FIG. 4B, it is determined whether bulk tungsten hasbeen deposited to an adequate thickness. If not, operations 482-488 arerepeated until a desired thickness is deposited. In some embodiments,operations 482-488 are repeated until a feature is filled. In someembodiments, operation 499 is also repeated in combination withoperations 482-488 when repeating the deposition cycle to deposit bulktungsten by sequential CVD.

FIG. 4C provides a process flow diagram for a method performed inaccordance with disclosed embodiments. In operation 480, bulk tungstenis deposited by sequential CVD. The process conditions and chemistriesmay be any of those described above with respect to FIGS. 4B and 5A-5J.In operation 498, bulk tungsten is deposited by non-sequential CVD.During non-sequential CVD, a substrate is exposed to atungsten-containing precursor and a reducing agent simultaneously todeposit bulk tungsten. Example tungsten-containing precursors includefluorine-containing precursors (e.g., WF₆), chlorine-containingprecursors (e.g., WCl_(x)), and tungsten hexacarbonyl (W(CO)₆). Examplereducing agents include hydrogen. In some embodiments, non-sequentialCVD is deposited by exposing the substrate to WF₆ and H₂. Operations 480and 498 may be performed sequentially, or any of operation 480 may beperformed one or more times before or after performing operation 498. Insome embodiments, operations 480 and 498 are performed in pulses, suchthat operation 498 is performed every 2 or more cycles of performingoperation 480. Bulk tungsten may thus be deposited using a combinationof sequential CVD and non-sequential CVD. In operation 499, thesubstrate is exposed to nitrogen. In some embodiments, operation 499 isperformed in combination with operation 480, 498, or both. In variousembodiments, the substrate is exposed to nitrogen continuously duringoperations 480, 498, or both. In various embodiments, the substrate isexposed to pulses of nitrogen during operations 480, 498, or both. Invarious embodiments, oxygen or another nitrogen-containing gas such asammonia is used instead of or in combination with nitrogen. Operations480, 498, and 499 may be performed sequentially, or any of operation 480or 499 may be performed one or more times before or after performingoperation 498. In some embodiments, operation 480 and 498 and 499 areperformed in pulses, such that operation 498 is performed every 2 ormore cycles of performing operation 480, which is performed every 2 ormore cycles of performing operation 499. Bulk tungsten may thus bedeposited using a combination of sequential CVD and non-sequential CVDwith continuous exposure to nitrogen, oxygen and combinations thereof.Bulk tungsten may thus be deposited using a combination of sequentialCVD and non-sequential CVD with periodic pulses of exposure to nitrogen,oxygen, ammonia, and combinations thereof.

FIG. 4D provides a process flow diagram for a method performed inaccordance with disclosed embodiments. In operation 420, a substratehaving adjacent V-shaped features is provided. V-shaped features are asdefined above with respect to FIGS. 3H and 3I. The distance betweenadjacent features on the substrate is no greater than a distance betweenabout 20 nm and about 40 nm. In operation 430, a first amount of metalis deposited in the V-shaped features. In various embodiments, the metalis tungsten. In some embodiments, the metal is ruthenium, or cobalt, ormolybdenum. The metal is deposited using any suitable technique, such asCVD, ALD, sequential CVD, and the like. In some embodiments, the metalis tungsten deposited by sequential CVD using a tungsten-containingprecursor such as WF₆, WCl₆, or WCl₅. In operation 439, the substrate isexposed to an inhibition gas, which may be nitrogen, oxygen, ammonia, orcombinations thereof depending on the metal to be deposited, thetechnique used to deposit it, and the precursor used to deposit it. Forexample, in some embodiments, the inhibition gas is nitrogen, and themetal deposited is tungsten using WF₆ as the tungsten-containingprecursor. As noted above, it will be understood that if ammonia is usesas the inhibition gas and WF₆ as the tungsten-containing precursor fordepositing tungsten, exposures to the inhibition gas and exposure to WF₆to deposit the tungsten are separate temporally to reduce reactionbetween ammonia and WF₆. It will be understood that operation 439 may bepart of operation 430 such that during deposition of the first amount ofmetal, the substrate is periodically or continuously exposed to aninhibition gas. Such examples are described further below with respectto FIGS. 8-11. In operation 440, a second amount of metal is depositedover the first amount of metal. Any suitable deposition technique may beused. In some embodiments, operation 440 is performed after performing439. For example, in one embodiment, a first amount of tungsten isdeposited by CVD, the deposited tungsten is exposed to nitrogen, and asecond amount of tungsten is deposited over the nitrogen-exposeddeposited tungsten to fill a V-shaped feature. In some embodiments,operation 439 is performed as part of operation 440. For example, wherethe second amount of metal is deposited by sequential CVD, theinhibition gas may be flowed with pulses of hydrogen, or with pulses ofargon, or pulses of the tungsten-containing precursor, or continuouslythroughout a sequential CVD cycle, where a sequential CVD cycle includesthe operations of exposure to hydrogen, exposure to argon, exposure to atungsten-containing precursor, and exposure to argon.

Disclosed embodiments are suitable for reducing line bending. Linebending analysis is performed by measuring the line width and roughnessof the trenches filled with metal (i.e. tungsten). The line bendinganalysis involves imaging the metal at the top of the device openingwith plan-view microscopy and measuring the metal width at multiplepoints on multiple lines. For each line, the line width is measuredacross 100 points. From each line, one then calculates the average linewidth and the variation of the line width, which may also be defined asroughness. The “line width mean” is the average of all the individuallines' average line width measured during analysis.

For line bending, two main metrics are defined as follows: (i)line-to-line (LTL) variation is the standard deviation of the averageline widths, thereby capturing the variation of line width changesacross different lines on the image, and (ii) line width roughness (LWR)is the average of line roughness (variation of line width within eachline) from all the measured lines, thereby capturing the average linewidth variation within single lines. These two metrics, LTL and LWR arecombined into single variation metric, σ total, as determined by σ=(σ₁²+σ₂ ²)^(1/2). Furthermore, LTL and σ total are normalized with respectto line width mean, described as LTL % and σ total %.

In various embodiments, disclosed embodiments result in substrates wheretotal variance is less than about 5 nm, or less than about 1.5 nm, or inpercentage, less than about 7.2%, where total variance percentage iscalculated by normalizing total variance by the average line width. Anexperiment conducted to determine thickness of films versus line bendingfor top down SEM/top of trench images showed that as thickness of themetal increases in V-shaped features or trenches such as shown in anddescribed above with respect to FIGS. 3H and 3I, line bending phenomenonbecomes more severe. This analysis was based on a top down SEM/top oftrench analysis.

Nitrogen exposure to reduce line bending can be used during depositionof the tungsten nucleation layer and/or bulk tungsten. For example,referring to FIG. 4A, nitrogen exposure may be performed during any ofoperations 402, 404, 406, 408, and combinations thereof, or during allof operations 402-408. Referring to FIG. 4B, nitrogen exposure may beperformed during any of operations 482, 484, 486, 488, and combinationsthereof, or during all of operations 482-488. In some embodiments,nitrogen exposure is performed during bulk tungsten deposition bysequential CVD to reduce line bending when features are being filled ona substrate with bulk tungsten.

FIGS. 5A-5J are schematic illustrations of an example mechanism forcycles of sequential CVD. It will be understood that FIGS. 5A-5J do notinclude example mechanisms for nitrogen exposure; such example isprovided in FIG. 6.

FIG. 5A depicts an example mechanism where H₂ is introduced to thesubstrate 500, which has a tungsten nucleation layer 501 depositedthereon. Hydrogen is introduced in gas phase (511 a and 511 b) and someH₂ (513 a and 513 b) is on the surface of the tungsten nucleation layer301, but may not necessarily adsorb onto the surface. For example, H₂may not necessarily chemisorb onto the nucleation layer 501, but in someembodiments, may physisorb onto the surface of the nucleation layer 501.

FIG. 5B shows an example illustration whereby H₂ previously in gas phase(511 a and 511 b in FIG. 5A) are purged from the chamber, and H₂previously on the surface (513 a and 513 b) remain on the surface of thetungsten nucleation layer 501.

FIG. 5C shows an example schematic for operation 486 of FIG. 4B. In FIG.5C, the substrate is exposed to WF₆, some of which is in gas phase (531a and 531 b) and some of which is at or near the surface of thesubstrate (523 a and 523 b).

As described above with respect to operation 486 of FIG. 4B, and asshown in the example depicted in FIG. 5D, WF₆ may react with H₂ totemporarily form intermediate 543 b, whereby in FIG. 5E, intermediate543 b fully reacts to leave tungsten 590 on the surface of the substrate500 on the nucleation layer 501, and HF in gas phase (551 a and 551 b,for example).

As described above with respect to operation 486 of FIG. 4B, and asshown in FIG. 5D, WF₆ may partially react with H₂ to form intermediate543 a, whereby in FIG. 5E, intermediate 543 a remains partially reactedon the surface of the substrate 500 on the nucleation layer 501. Thereaction mechanism involving WF₆ and H₂ may be slower than a reactionbetween a borane or a silane or a germane with WF₆ for deposition of atungsten nucleation layer due to activation energy barriers and stericeffects. For example, without being bound by a particular theory, thestoichiometry of WF₆ may use at least three H₂ molecules to react withone molecule of WF₆. It is possible that WF₆ partially reacts withmolecules of H₂ but rather than forming tungsten, an intermediate isformed. For example, this may occur if there is not enough Thin itsvicinity to react with WF₆ based on stoichiometric principles (e.g.,three H₂ molecules are used to react with one molecule of WF₆) therebyleaving an intermediate 543 a on the surface of the substrate.

FIG. 5F provides an example schematic of the substrate when the chamberis purged. Note that compound 543 c may be an intermediate formed butnot completely reacted, while some tungsten 590 may be formed on thesubstrate. Each cycle thereby forms a sub-monolayer of tungsten on thesubstrate.

As an example, FIG. 5G shows operation 482 of FIG. 4B in the repeatedcycle, whereby H₂ 511 c in gas phase is introduced to the substrate withthe deposited tungsten 590 and the partially reacted intermediate 543 dthereon. Note that the H₂ introduced may now fully react with theintermediate 543 d on the substrate such that, as shown in FIG. 5H, thereacted compound 543 d leaves behind deposited tungsten 590 b and 590 c,and byproducts HF 551 c and 551 d are formed in gas phase. Some H₂ 511 cmay remain in gas phase, while some H₂ 513 c may remain on the tungstenlayer 590 a. In Figure SI, the chamber is purged (thereby correspondingwith operation 484 of FIG. 4B), leaving behind deposited tungsten 590 a,590 b, and 590 c, and some H₂ 513 c. In FIG. 5J, WF₆ is again introducedin a dose such that molecules 531 c and 523 c may then adsorb and/orreact with H₂ and the substrate. FIG. 5J may correspond to operation 486of FIG. 4B. After the WF₆ dose, the chamber may again be purged andcycles may be repeated again until the desired thickness of tungsten isdeposited.

Tungsten films deposited using disclosed embodiments have low fluorineconcentrations, such as about two orders of magnitude less fluorineconcentration than tungsten deposited by non-sequential CVD. Depositionconditions, such as temperature, pulse times, and other parameters, mayvary depending on hardware or process modifications. Overall tensilestress of films may be less than about 1 GPa.

FIG. 6 shows an example of a substrate having a V-shaped feature 603where nitrogen 670 on the surface of the deposited tungsten 650 alongthe sidewalls of the feature 603 prevents tungsten-tungsten bonding,thereby reducing line bending. Without being bound by a particulartheory, it is believed that when additional tungsten is deposited,nitrogen desorbs and therefore little to no nitrogen is incorporatedinto the deposited tungsten film. Disclosed embodiments are suitable fordepositing metal such as tungsten into multiple features, the featuresbeing spaced apart on a substrate where the pitch between adjacentfeatures is between about 20 nm and about 40 nm.

FIGS. 7-11 provide example timing sequence diagrams for example cyclesof performing certain disclosed embodiments for variations of continuousand pulsed nitrogen exposure in accordance with various embodiments.

FIG. 7 provides a timing sequence diagram depicting examples cycles ofsequential CVD in a process 700 including periodic nitrogen exposureduring each sequential CVD cycle. The phases depicted in the example inFIG. 7 includes various process parameters, such as carrier gas or purgegas flow, hydrogen flow, WF₆ flow (used as an example of atungsten-containing precursor for depositing tungsten; other suitablemetal-containing precursors may be used for depositing a suitable metal,such as ruthenium, or cobalt, or molybdenum), and nitrogen gas flow. Thelines indicate when the flow is turned on and off. Note that in variousembodiments, plasma is not ignited and is not depicted as a processparameter. Additional process parameters which are not depicted in FIG.7 but may be modulated as necessary include substrate temperature andprocess chamber pressure.

Process 700 includes two deposition cycles 711A and 711B but it will beunderstood that more than two deposition cycles may be used in certaindisclosed embodiments. Deposition cycle 711A includes five phases,including a nitrogen dose 799A, hydrogen dose 720A, purge phase 740A,WF₆ dose 760A, and purge phase 770A. Nitrogen dose 799A may correspondto operation 499 of FIG. 4B. During nitrogen dose 799A, the carrier gasflow may be turned on. Hydrogen gas flow and WF₆ gas flows are turnedoff and nitrogen flow is turned on. Hydrogen dose 720A may correspond tooperation 482 of FIG. 4B. During hydrogen dose 799A, the carrier gasflow may be turned on. Hydrogen gas flow is turned on, while WF₆ gasflow and nitrogen gas flows are turned off. Purge phase 740A maycorrespond to operation 484 of FIG. 4B. During purge phase 740A, thecarrier gas may continue to flow to act as a purge gas. In someembodiments, this involves allowing the carrier gas to flow into thechamber instead of diverting it as it may be diverted during a nitrogen,hydrogen, or WF₆ gas flow. During purge phase 740A, hydrogen, WF₆, andnitrogen gas flows are turned off. Tungsten hexafluoride dose 760A maycorrespond to operation 486 of FIG. 4B. Although WF₆ is depicted in FIG.7, it will be understood that other tungsten-containing precursors maybe used. Additionally, although tungsten is mentioned in combinationwith FIG. 7, it will be understood that other metal-containingprecursors may be used to deposit other metal. For example,ruthenium-containing precursors may be used to deposit ruthenium,molybdenum-containing precursors may be used to deposit molybdenum, andcobalt-containing precursors may be used to deposit cobalt. During WF₆dose 760A, the carrier gas may be flowed to introduce the WF₆ gas intothe chamber, and WF₆ flow is also turned on. During this dose, hydrogenand nitrogen flows are turned off. Purge phase 770A may correspond tooperation 488 of FIG. 4B. During purge phase 770A, carrier gas flow isturned on as the carrier gas acts as a purge gas, while hydrogen gasflow, WF₆ gas flow, and nitrogen gas flows are turned off.

It is determined as depicted in operation 490 of FIG. 4B thatinsufficient tungsten has been deposited, and the deposition cycle isrepeated as depicted in deposition cycle 711B. Deposition cycle 711Bincludes nitrogen dose 799B, hydrogen dose 720B, purge phase 740B, WF₆dose 760B, and purge phase 770B. During nitrogen dose 799B, nitrogen gasflow and carrier gas flow are turned on while hydrogen gas flow and WF₆gas flow are turned off. During hydrogen dose 720B, carrier gas flow andhydrogen gas flows are turned on while WF₆ gas flow and nitrogen gasflows are turned off. During purge phase 740B, carrier gas flow remainson while hydrogen gas flow, WF₆ gas flow, and nitrogen gas flow areturned off. During WF₆ dose 760B, carrier gas flow and WF₆ gas flow areturned on while hydrogen gas and nitrogen gas flows are turned off.During purge phase 770B, carrier gas flow remains on while hydrogen gas,WF₆ gas, and nitrogen gas flows are turned off.

FIGS. 8-11 show example tungsten deposition cycle pulse sequences. Suchcycles may be ALD or sequential CVD deposition cycles. Although fourexamples are depicted, these examples are not limiting. While N₂ isdepicted in these examples, it will be understood that in someembodiments oxygen or ammonia may be used instead. Although WF₆ isdepicted in FIGS. 8-11, it will be understood that othertungsten-containing precursors may be used. Additionally, althoughtungsten is mentioned in combination with FIGS. 8-11, it will beunderstood that other metal-containing precursors may be used to depositother metal. For example, ruthenium-containing precursors may be used todeposit ruthenium, molybdenum-containing precursors may be used todeposit molybdenum, and cobalt-containing precursors may be used todeposit cobalt.

The sequence shown in FIG. 8 shows a process 800 where N₂ continuouslyflows during sequential CVD whereby a tungsten-containing precursor andreducing agent H₂ are pulsed alternately with purge or carrier gas suchas argon flowed between pulses. FIG. 8 depicts a process 800 having twodeposition cycles 811A and 811B. Deposition cycle 811A includes hydrogendose 820A, purge phase 840A, WF₆ dose 860A, and purge phase 870A.Throughout the deposition cycles 811A and 811B, nitrogen is continuouslyflowed. During hydrogen dose 820A, carrier gas, hydrogen, and nitrogengas flows are on while WF₆ gas flow is turned off. During purge phase840A, carrier gas and nitrogen gas flows are on while H₂ and WF₆ gasflows are turned off. Given that the gas used to preventtungsten-tungsten bonding in this example is flowed continuously and WF₆is used as the example tungsten-containing precursor, it will beunderstood that NH₃ would not be used to flow continuously to reduce thetungsten-tungsten bonding to avoid a reaction between NH₃ and WF₆ thatmay result in undesirable by-products. During WF₆ dose 860A, carriergas, WF₆ gas, and nitrogen gas flows are turned on while H₂ gas isturned off. During purge phase 870A, carrier gas and nitrogen gas flowsare turned on while H₂ and WF₆ gas flows are turned off. The cycle isrepeated in deposition cycle 811B, which includes hydrogen dose 820B,purge phase 840B, WF₆ dose 860B, and purge phase 870B. During hydrogendose 820B, like hydrogen dose 820A, carrier gas, hydrogen, and nitrogengas flows are on while WF₆ gas flow is turned off. During purge phase840B, carrier gas and nitrogen gas flows are on while H₂ and WF₆ gasflows are turned off. During WF₆ dose 860B, carrier gas, WF₆, andnitrogen gas flows are on while H₂ gas flow is turned off. During purgephase 870B, carrier gas and nitrogen gas flows remain on while hydrogenand WF₆ gas flows are turned off.

The sequence shown in FIG. 9 shows a process 900 where N₂ used during areducing agent H₂ dose. FIG. 9 depicts a process 900 having twodeposition cycles 911A and 911B. Deposition cycle 911A includes hydrogendose 920A, purge phase 940A, WF₆ dose 960A, and purge phase 970A. Duringhydrogen dose 920A, carrier gas, hydrogen, and nitrogen gas flow areturned on while WF₆ gas flow is turned off. During purge phase 940A,carrier gas flow is turned on while H₂, WF₆, and nitrogen gas flows areturned off. During WF₆ dose 960A, carrier gas flow and WF₆ gas flows areturned on while hydrogen and nitrogen gas flows remain off. During purgephase 970A, carrier gas flow remains on while H₂, WF₆, and nitrogen gasflows are turned off. The cycle is repeated in deposition cycle 911B,which includes hydrogen dose 920B, purge phase 940B, WF₆ dose 960B, andpurge phase 970B. During hydrogen dose 920B, carrier gas, hydrogen gas,and nitrogen gas flows are on while WF₆ gas flow is turned off. Duringpurge phase 940B, carrier gas flow remains on while H₂, WF₆, and N₂ gasflows are turned off. During WF₆ dose 960B, carrier gas and WF₆ gasflows are on while H₂ and nitrogen gas flows are turned off. Duringpurge phase 970B, carrier gas flow remains on while H₂, WF₆, and N₂ gasflows are turned off.

The sequence shown in FIG. 10 shows a process 1000 where N₂ used duringargon pulses that are used after a reducing agent H₂ dose and prior to atungsten-containing precursor dose. Deposition cycle 1011A includeshydrogen dose 1020A, purge phase 1040A, WF₆ dose 1060A, and purge phase1070A. During hydrogen dose 1020A, carrier gas and hydrogen gas flowsare on while WF₆ and nitrogen gas flows are off. During purge phase1040A, carrier gas and nitrogen gas flows are turned on, while hydrogenand WF₆ gas flows are turned off. During WF₆ dose 1060A, carrier gas andWF₆ gas flows are turned on while hydrogen and nitrogen gas flows areturned off. During purge phase 1070A, carrier gas flow remains on whileH₂, WF₆, and N₂ gas flows are turned off. The cycle is repeated indeposition cycle 1011B, which includes hydrogen dose 1020B, purge phase1040B, WF₆ dose 1060B, and purge phase 1070B. During hydrogen dose1020B, carrier gas and hydrogen gas flows are turned on while WF₆ andnitrogen gas flows remain off. During purge phase 1040B, carrier gas isflowed with nitrogen gas, and nitrogen gas and WF₆ gas flows are turnedoff. During WF₆ dose 1060B, carrier gas and WF₆ gas flows are on whilehydrogen and nitrogen gas flows are turned off. During purge phase1070B, carrier gas flow is on while H₂, WF₆, and N₂ gas flows are off.

The sequence shown in FIG. 11 shows N₂ used during argon pulses that areused prior to a reducing agent H₂ dose and after a tungsten-containingprecursor dose. Deposition cycle 1111A includes hydrogen dose 1120A,purge phase 1140A, WF₆ dose 1160A, and purge phase 1170A. Duringhydrogen dose 1120A, carrier gas and hydrogen gas flows are turned onwhile WF₆ and nitrogen gas flows are turned off. During purge phase1140A, carrier gas flow is on while H₂, WF₆, and N₂ gas flows are turnedoff. During WF₆ dose 1160A, carrier gas and WF₆ gas flows are turned onwhile hydrogen and nitrogen gas flows are turned off. During purge phase1170A, carrier gas and nitrogen gas flows are turned on while hydrogenand WF₆ gas flows are turned off. The cycle is repeated in depositioncycle 1111B, which includes hydrogen dose 1120B, purge phase 1140B, WF₆dose 1160B, and purge phase 1170B. During hydrogen dose 1120B, carriergas and hydrogen gas flows are turned on while WF₆ and nitrogen gasflows are turned off. During purge phase 1140B, carrier gas flow remainson while H₂, WF₆, and nitrogen gas flows are turned off. During WF₆ dose1160B, carrier gas and WF₆ gas flows are on while hydrogen and nitrogengas flows are off. During purge phase 1170B, carrier gas and nitrogengas flows are turned on while hydrogen and WF₆ gas flows are turned off.

While WF₆ is depicted in these examples, it will be understood thatother tungsten-containing precursors may be used such as WCl₆, and/orWCl₅. Additionally, for depositing other metals such as ruthenium,molybdenum, or cobalt, a suitable ruthenium-containing precursor,molybdenum-containing precursor, or cobalt-containing precursor may beused, respectively.

Disclosed embodiments may have various applications in tungstendeposition processes. For example, in some embodiments, a feature may befilled by depositing a tungsten nucleation layer by ALD cycles ofalternating pulses of a reducing agent (e.g., a borane, a silane, or agermane) and WF₆ with periodic exposure to nitrogen, followed by bulktungsten deposition by sequential CVD with periodic exposure to nitrogenas described above with respect to FIG. 4B.

In another example, in some embodiments, a tungsten nucleation layer maybe deposited using ALD cycles of a reducing agent and WF₆, followed bybulk tungsten deposition using a combination of CVD of fluorine-freetungsten using a reducing agent and a fluorine-free tungsten-containingprecursor (e.g., a metal-organic tungsten precursor), and sequential CVDas described above with respect to FIG. 4B where the substrate isperiodically exposed to nitrogen to prevent line bending. Fluorine-freetungsten precursors may also include tungsten carbonyl (W(CO)₆), andtungsten chlorides (WCl_(x)) such as tungsten pentachloride (WCl₅) andtungsten hexachloride (WCl₆).

In another example, a tungsten nucleation layer may be deposited on afeature by ALD cycles of alternating pulses of a reducing agent and WF₆,and tungsten bulk may be deposited by alternating between sequential CVDas described above with respect to FIG. 4B and non-sequential CVD wherethe substrate is periodically exposed to nitrogen to prevent linebending. For example, bulk tungsten may be deposited using a number ofcycles of sequential CVD between pre-determined durations ofnon-sequential CVD. In a specific example, bulk tungsten may bedeposited using about 5 cycles of sequential CVD, followed by 5 secondsof non-sequential CVD, followed by 5 cycles of sequential CVD, andanother 5 seconds of non-sequential CVD.

In another example, a feature may be filled by first depositing atungsten nucleation layer by ALD cycles of alternating pulses of areducing agent and WF₆, then partially filling the feature usingsequential CVD, and filling the rest of the feature by non-sequentialCVD where the substrate is periodically exposed to nitrogen to preventline bending.

In another example, a feature may be filled by depositing a tungstennucleation layer by ALD cycles of alternating pulses of a reducing agentand WF₆, followed by partial deposition of bulk tungsten by sequentialCVD, and complete bulk fill by CVD of fluorine-free tungsten (such asusing a metal-organic tungsten precursor) where the substrate isperiodically exposed to nitrogen to prevent line bending. For example, anumber of cycles of sequential CVD may be performed to partially fill afeature with bulk tungsten, followed by CVD using simultaneous exposureto MDNOW and H₂ to fill the rest of the feature. Note in someembodiments, a feature may be filled without depositing a nucleationlayer, but a nucleation layer may help reduce growth delay of bulktungsten.

It will be understood that various combinations of the applicationsdescribed herein may be used to deposit tungsten and methods are notlimited to the examples provided herein where the substrate isperiodically exposed to nitrogen to prevent line bending. For example,chlorine-containing tungsten precursors (WCl_(x)) such as tungstenpentachloride (WCl₅) and tungsten hexachloride (WCl₆) may be usedinstead of or in combination with WF₆ in embodiments described herein.

In various embodiments, a soak or surface treatment operation may beperformed prior to depositing a nucleation layer. Example soak orsurface treatments include exposing the substrate to silane (SiH₄),disilane (Si₂H₆), trisilane (Si₃H₈), germane (GeH₄), argon (Ar),tungsten hexafluoride (WF₆), diborane (B₂H₆), hydrogen (H₂), nitrogen(N₂) gas, or combinations thereof. In some embodiments, the substratemay be soaked using one or more gases. For example, in some embodiments,the substrate may be exposed to silane for a first duration, and thenexposed to diborane for a second duration. Such operations may also berepeated in cycles. In another example, the substrate may be exposed todiborane for a first duration, and then exposed to silane for a secondduration. In another example, the substrate may be exposed to diboranefor a first duration, and then exposed to hydrogen for a secondduration. In another example, the substrate may be exposed to silane fora first duration, and then exposed to hydrogen for a second duration. Insome embodiments, the substrate may be exposed to nitrogen gas incombination with any of the above described soaking processes. In any ofthe disclosed embodiments, a chamber housing the substrate may be purgedbetween one or more soak operations. Purging may be performed by flowingan inert gas such as argon into the chamber. For example, in oneexample, the substrate may be exposed to diborane for a first duration,the chamber may then be purged, and then the substrate may be exposed tosilane for a second duration.

Nucleation layers deposited in accordance with certain disclosedembodiments prior to deposition of a bulk tungsten layer may bedeposited by alternating between a tungsten-containing precursor and areducing agent, such as silane (SiH₄), disilane (Si₂H₆), trisilane(Si₃H₈), germane (GeH₄), or diborane (B₂H₆). In some embodiments, thenucleation layer is deposited by exposing the substrate to alternatingpulses of a tungsten-containing precursor and silane. In someembodiments, the nucleation layer is deposited by exposing the substrateto alternating pulses of a tungsten-containing precursor and diborane.In some embodiments, the nucleation layer is deposited by exposing thesubstrate to alternating pulses of a tungsten-containing precursor andsilane, then exposing the substrate to alternating pulses of atungsten-containing precursor and diborane. In some embodiments, thenucleation layer is deposited by exposing the substrate to alternatingpulses of a tungsten-containing precursor and diborane, then exposingthe substrate to alternating pulses of a tungsten-containing precursorand silane. In some embodiments, the nucleation layer is deposited byexposing the substrate to alternating pulses of a tungsten-containingprecursor and silane, then exposing the substrate to alternating pulsesof a tungsten-containing precursor and diborane, then exposing thesubstrate to alternating pulses of a tungsten-containing precursor andsilane. In some embodiments, the nucleation layer is deposited byexposing the substrate to alternating pulses of a tungsten-containingprecursor and diborane, then exposing the substrate to alternatingpulses of a tungsten-containing precursor and silane, then exposing thesubstrate to alternating pulses of a tungsten-containing precursor anddiborane. In any of the disclosed embodiments, a chamber housing thesubstrate may be purged between one or more dose operations fordepositing a nucleation layer. Purging may be performed by flowing aninert gas such as argon into the chamber. Any suitable inert gas may beused for purging. For example, in some embodiments, a substrate may beexposed to a pulse of tungsten-containing precursor, then the chambermay be purged, then the substrate may be exposed to a pulse of silane,and the chamber may be purged again, and such operations may be repeatedin cycles.

Nucleation layer deposition that may be used in any of the abovedescribed implementations may include co-flowing any one of hydrogen(H₂), argon (Ar), nitrogen (N₂), or combinations thereof during theentire nucleation deposition process, or during a silane dose, or duringa diborane dose, or during a tungsten-containing precursor dose such asWF₆ dose, or during any purge times. In some embodiments, a surfacetreatment operation may be performed during or after nucleation growthby exposing the substrate to any of silane, disilane, trisilane,germane, diborane, hydrogen, tungsten hexafluoride, nitrogen, argon, andcombinations thereof. For example, during deposition of a nucleationlayer, the substrate may be exposed to alternating pulses of silane andWF₆, then the substrate may be exposed to a silane soak, then thesubstrate may resume being exposed to alternating pulses of silane andWF₆. Such operations may be performed in cycles. For example, in someembodiments, the following cycle may be repeated one or more times todeposit a nucleation layer: alternating pulses of SiH₄ and WF₆ andexposure to a surface treatment.

In some embodiments, the nucleation layer may be deposited by exposingthe substrate to any combination of the tungsten-containing precursorand any one or more of the following gases in any sequence and order, inone or more cycles: diborane, silane, disilane, trisilane, hydrogen,nitrogen, and germane (GeH₄). For example, in some embodiments, anucleation layer may be deposited by exposing the substrate to diborane,exposing the substrate to tungsten hexafluoride, exposing the substrateto silane, and exposing the substrate to hydrogen. Such operations maybe repeated in one or more cycles. In another example, in someembodiments, a nucleation layer may be deposited by exposing thesubstrate to silane, exposing the substrate to tungsten hexafluoride,and exposing the substrate to hydrogen. Such operations may be repeatedin one or more cycles. In another example, in some embodiments, anucleation layer may be deposited by exposing the substrate to diborane,exposing the substrate to hydrogen, and exposing the substrate totungsten hexafluoride. Such operations may be repeated in one or morecycles. In another example, in some embodiments, a nucleation layer maybe deposited by exposing the substrate to nitrogen, exposing thesubstrate to diborane, and exposing the substrate to tungstenhexafluoride. Such operations may be repeated in one or more cycles. Inanother example, in some embodiments, a nucleation layer may bedeposited by exposing the substrate to silane, exposing the substrate tonitrogen, and exposing the substrate to tungsten hexafluoride. Suchoperations may be repeated in one or more cycles. In any of thedescribed embodiments, the substrate may be exposed to surface treatmentand/or soaking operations before, during, or after deposition of thenucleation cycle using any available gas. In some embodiments,additional gases may be co-flowed with any of the above described gasesduring one or more exposures of the nucleation deposition process. Inany of the disclosed embodiments, a chamber housing the substrate may bepurged between one or more dose operations for depositing a nucleationlayer. Purging may be performed by flowing an inert gas such as argoninto the chamber. Any suitable inert gas may be used for purging. Itwill be understood that in some embodiments, the substrate may beperiodically exposed to nitrogen during deposition of a tungstennucleation layer.

Bulk tungsten deposition may be deposited using any of the disclosedembodiments described herein and in U.S. patent application Ser. No.14/723,275 (Attorney Docket No. LAMRP183/3623-1US) filed on May 27,2015, which is herein incorporated by reference in its entirety. In anyof the above described implementations, bulk tungsten may also bedeposited periodically, with re-nucleation and/or soak and/or surfacetreatment and/or conventional CVD deposition operations performedbetween bulk depositions. For example, in some embodiments, bulktungsten may be deposited using disclosed embodiments as described abovewith respect to FIG. 4B, then bulk tungsten deposition may be paused,then the substrate may be exposed to alternating pulses of silane andWF₆, or diborane and WF₆ to re-nucleate the surface of the substrate,then the bulk tungsten deposition may be resumed using disclosedembodiments as described above with respect to FIG. 4B. Such operationsmay be repeated in any number of cycles. In another example, in someembodiments, bulk tungsten may be deposited using disclosed embodimentsas described above with respect to FIG. 4B, then bulk tungstendeposition may be paused, then the substrate may be exposed to a soak orsurface treatment by flowing any of silane, disilane, trisilane,germane, diborane, hydrogen, tungsten hexafluoride, nitrogen, argon, andcombinations thereof, to treat the surface of the substrate, then thebulk tungsten deposition may be resumed using disclosed embodiments asdescribed above with respect to FIG. 4B. Bulk tungsten deposition may beperformed by exposing the substrate to a tungsten-containing precursorsuch as WF₆ and any one or more of the following gases: hydrogen,silane, disilane, trisilane, diborane, nitrogen, argon, and germane.Bulk tungsten may also be deposited using a combination of sequentialCVD and conventional CVD as described above. Conventional CVD may beperformed before, during (such as by cycling between sequential andconventional CVD), or after depositing bulk tungsten using sequentialCVD. It will be understood that in some embodiments, the substrate maybe periodically exposed to nitrogen during deposition of a tungsten bulklayer.

In some embodiments, the substrate may be annealed at any suitabletemperature before depositing bulk tungsten and after depositing thenucleation layer. In some embodiments, the substrate may be annealed atany suitable temperature after depositing the bulk tungsten layer. Insome embodiments, the substrate may be annealed at any suitabletemperature during intermediate times during deposition of the bulktungsten. Annealing may be performed in any suitable gas environment,such as an environment including one or more of the following gases:tungsten-containing gas such as WF₆, hydrogen, silane, disilane,trisilane, diborane, nitrogen, argon, and germane.

In various embodiments, the chamber housing the substrate may be pumpedor purged before or after doses of the tungsten-containing precursor andreducing agent for depositing bulk tungsten in accordance with disclosedembodiments as described above with respect to FIG. 4B. In someembodiments, delay time may be incorporated into a dose or purge step ofsequential CVD deposition as described herein. In some embodiments, oneor more gases may be co-flowed during a dose or purge operation usingone or more of any of the following gases: WF₆, hydrogen, silane,disilane, trisilane, diborane, nitrogen, argon, and germane.

The temperature of the substrate during nucleation deposition may not bethe same as the temperature of the substrate during sequential CVD asdescribed above with respect to FIG. 4B. The temperature of thesubstrate will be understood to mean the temperature at which thepedestal holding the substrate is set. Disclosed embodiments may beperformed at any suitable pressure, such as pressures greater than about10 Torr, or pressures less than about 10 Torr. For a multi-stationchamber, each pedestal may be set at different temperatures. In someembodiments, each pedestal is set at the same temperature. Substratesmay be cycled from station to station during any or all of any of theabove described operations in accordance with disclosed embodiments.Chamber pressure may also be modulated in one or more operations ofcertain disclosed embodiments. In some embodiments, chamber pressureduring nucleation deposition is different from chamber pressure duringbulk deposition. In some embodiments, chamber pressure during nucleationdeposition is the same as the chamber pressure during bulk deposition.

During any of the above described exposures, the gases may be pulsed orflowed continuously. For example, in some embodiments, during a WF₆ doseof a sequential CVD operation, WF₆ may be pulsed one or more timesduring a single dose. Likewise, in some embodiments, during a purge, aninert gas may be pulsed during one or more times during a single purgeoperation. Such pulsing operations may be performed during any operationof nucleation deposition or any operation of bulk deposition or anycombination thereof. In some embodiments, one or more changes to one ormore parameters such as pressure, flow rate, and temperature, may beused. In some embodiments, the pedestal may be moved during anyoperation of the nucleation deposition or bulk deposition or both suchthat the gap between the substrate and a showerhead over the pedestalmay be modulated. Moving the pedestal may be used in combination withaltering one or more parameters such as pressure, temperature, or flowrate. Modulating the gap between the substrate and the showerhead canaffect the pressure, temperature, or flow rate that may be used inaccordance with certain disclosed embodiments. It will be understoodthat any of the processes described herein may be applicable totechniques involving ALD.

Apparatus

Any suitable chamber may be used to implement the disclosed embodiments.Example deposition apparatuses include various systems, e.g., ALTUS® andALTUS® Max, available from Lam Research Corp., of Fremont, Calif., orany of a variety of other commercially available processing systems. Insome embodiments, sequential chemical vapor deposition (CVD) may beperformed at a first station that is one of two, five, or even moredeposition stations positioned within a single deposition chamber. Thus,for example, hydrogen (H₂) and tungsten hexafluoride (WF₆) may bealternately introduced to the surface of the semiconductor substrate, atthe first station, using an individual gas supply system that creates alocalized atmosphere at the substrate surface. Another station may beused for fluorine-free tungsten deposition, or non-sequential CVD.Another station may be used to deposit the tungsten nucleation layer atlow pressure. Another station may be used for periodic nitrogenexposure. In some embodiments, periodic nitrogen exposure is performedin the same station as deposition. Two or more stations may be used todeposit tungsten in a parallel processing. Alternatively a wafer may beindexed to have deposition operations performed over two or morestations sequentially.

FIG. 12 is a block diagram of a processing system suitable forconducting tungsten thin film deposition processes in accordance withembodiments. The system 1200 includes a transfer module 1203. Thetransfer module 1203 provides a clean, pressurized environment tominimize risk of contamination of substrates being processed as they aremoved between various reactor modules. Mounted on the transfer module1203 is a multi-station reactor 1209 capable of performing atomic layerdeposition (ALD), and sequential CVD with nitrogen or inhibition gasexposure according to embodiments. Multi-station reactor 1209 may alsobe used to perform fluorine-free tungsten deposition and/ornon-sequential CVD in some embodiments. Reactor 1209 may includemultiple stations 1211, 1213, 1215, and 1217 that may sequentiallyperform operations in accordance with disclosed embodiments. Forexample, reactor 1209 could be configured such that station 1211performs nucleation layer deposition by ALD, station 1213 performssequential CVD, station 1215 performs fluorine-free tungsten deposition,and station 1217 performs non-sequential CVD. Stations may be configuredto expose the wafer to periodic pulses or continuous flow of nitrogen,oxygen, or ammonia gas to prevent line bending on the substrate.Stations may include a heated pedestal or substrate support, one or moregas inlets or showerhead or dispersion plate. An example of a depositionstation 1300 is depicted in FIG. 13, including substrate support 1302and showerhead 1303. A heater may be provided in pedestal portion 1301.

Also mounted on the transfer module 1203 may be one or more single ormulti-station modules 1207 capable of performing plasma or chemical(non-plasma) pre-cleans. The module may also be used for varioustreatments to, for example, prepare a substrate for a depositionprocess. The system 1200 also includes one or more wafer source modules1201, where wafers are stored before and after processing. Anatmospheric robot (not shown) in the atmospheric transfer chamber 1219may first remove wafers from the source modules 1201 to loadlocks 1221.A wafer transfer device (generally a robot arm unit) in the transfermodule 1203 moves the wafers from loadlocks 1221 to and among themodules mounted on the transfer module 1203.

In various embodiments, a system controller 1229 is employed to controlprocess conditions during deposition. The controller 1229 will typicallyinclude one or more memory devices and one or more processors. Aprocessor may include a CPU or computer, analog and/or digitalinput/output connections, stepper motor controller boards, etc.

The controller 1229 may control all of the activities of the depositionapparatus. The system controller 1229 executes system control software,including sets of instructions for controlling the timing, mixture ofgases, chamber pressure, chamber temperature, wafer temperature, radiofrequency (RF) power levels, wafer chuck or pedestal position, and otherparameters of a particular process. Other computer programs stored onmemory devices associated with the controller 1229 may be employed insome embodiments.

Typically there will be a user interface associated with the controller1229. The user interface may include a display screen, graphicalsoftware displays of the apparatus and/or process conditions, and userinput devices such as pointing devices, keyboards, touch screens,microphones, etc.

System control logic may be configured in any suitable way. In general,the logic can be designed or configured in hardware and/or software. Theinstructions for controlling the drive circuitry may be hard coded orprovided as software. The instructions may be provided by “programming.”Such programming is understood to include logic of any form, includinghard coded logic in digital signal processors, application-specificintegrated circuits, and other devices which have specific algorithmsimplemented as hardware. Programming is also understood to includesoftware or firmware instructions that may be executed on a generalpurpose processor. System control software may be coded in any suitablecomputer readable programming language.

The computer program code for controlling the germanium-containingreducing agent pulses, hydrogen flow, and tungsten-containing precursorpulses, and other processes in a process sequence can be written in anyconventional computer readable programming language: for example,assembly language, C, C++, Pascal, Fortran, or others. Compiled objectcode or script is executed by the processor to perform the tasksidentified in the program. Also as indicated, the program code may behard coded.

The controller parameters relate to process conditions, such as, forexample, process gas composition and flow rates, temperature, pressure,cooling gas pressure, substrate temperature, and chamber walltemperature. These parameters are provided to the user in the form of arecipe, and may be entered utilizing the user interface.

Signals for monitoring the process may be provided by analog and/ordigital input connections of the system controller 1229. The signals forcontrolling the process are output on the analog and digital outputconnections of the deposition apparatus 1200.

The system software may be designed or configured in many differentways. For example, various chamber component subroutines or controlobjects may be written to control operation of the chamber componentsnecessary to carry out the deposition processes in accordance with thedisclosed embodiments. Examples of programs or sections of programs forthis purpose include substrate positioning code, process gas controlcode, pressure control code, and heater control code.

In some implementations, a controller 1229 is part of a system, whichmay be part of the above-described examples. Such systems can includesemiconductor processing equipment, including a processing tool ortools, chamber or chambers, a platform or platforms for processing,and/or specific processing components (a wafer pedestal, a gas flowsystem, etc.). These systems may be integrated with electronics forcontrolling their operation before, during, and after processing of asemiconductor wafer or substrate. The electronics may be referred to asthe “controller,” which may control various components or subparts ofthe system or systems. The controller 1229, depending on the processingrequirements and/or the type of system, may be programmed to control anyof the processes disclosed herein, including the delivery of processinggases, temperature settings (e.g., heating and/or cooling), pressuresettings, vacuum settings, power settings, radio frequency (RF)generator settings in some systems, RF matching circuit settings,frequency settings, flow rate settings, fluid delivery settings,positional and operation settings, wafer transfers into and out of atool and other transfer tools and/or load locks connected to orinterfaced with a specific system.

Broadly speaking, the controller may be defined as electronics havingvarious integrated circuits, logic, memory, and/or software that receiveinstructions, issue instructions, control operation, enable cleaningoperations, enable endpoint measurements, and the like. The integratedcircuits may include chips in the form of firmware that store programinstructions, digital signal processors (DSPs), chips defined asapplication specific integrated circuits (ASICs), and/or one or moremicroprocessors, or microcontrollers that execute program instructions(e.g., software). Program instructions may be instructions communicatedto the controller in the form of various individual settings (or programfiles), defining operational parameters for carrying out a particularprocess on or for a semiconductor wafer or to a system. The operationalparameters may, in some embodiments, be part of a recipe defined byprocess engineers to accomplish one or more processing steps during thefabrication of one or more layers, materials, metals, oxides, silicon,silicon dioxide, surfaces, circuits, and/or dies of a wafer.

The controller 1229, in some implementations, may be a part of orcoupled to a computer that is integrated with, coupled to the system,otherwise networked to the system, or a combination thereof. Forexample, the controller 1229 may be in the “cloud” or all or a part of afab host computer system, which can allow for remote access of the waferprocessing. The computer may enable remote access to the system tomonitor current progress of fabrication operations, examine a history ofpast fabrication operations, examine trends or performance metrics froma plurality of fabrication operations, to change parameters of currentprocessing, to set processing steps to follow a current processing, orto start a new process. In some examples, a remote computer (e.g. aserver) can provide process recipes to a system over a network, whichmay include a local network or the Internet. The remote computer mayinclude a user interface that enables entry or programming of parametersand/or settings, which are then communicated to the system from theremote computer. In some examples, the controller receives instructionsin the form of data, which specify parameters for each of the processingsteps to be performed during one or more operations. It should beunderstood that the parameters may be specific to the type of process tobe performed and the type of tool that the controller is configured tointerface with or control. Thus as described above, the controller maybe distributed, such as by including one or more discrete controllersthat are networked together and working towards a common purpose, suchas the processes and controls described herein. An example of adistributed controller for such purposes would be one or more integratedcircuits on a chamber in communication with one or more integratedcircuits located remotely (such as at the platform level or as part of aremote computer) that combine to control a process on the chamber.

Without limitation, example systems may include a plasma etch chamber ormodule, a deposition chamber or module, a spin-rinse chamber or module,a metal plating chamber or module, a clean chamber or module, a beveledge etch chamber or module, a physical vapor deposition (PVD) chamberor module, a CVD chamber or module, an ALD chamber or module, an atomiclayer etch (ALE) chamber or module, an ion implantation chamber ormodule, a track chamber or module, and any other semiconductorprocessing systems that may be associated or used in the fabricationand/or manufacturing of semiconductor wafers.

As noted above, depending on the process step or steps to be performedby the tool, the controller might communicate with one or more of othertool circuits or modules, other tool components, cluster tools, othertool interfaces, adjacent tools, neighboring tools, tools locatedthroughout a factory, a main computer, another controller, or tools usedin material transport that bring containers of wafers to and from toollocations and/or load ports in a semiconductor manufacturing factory.

The controller 1229 may include various programs. A substratepositioning program may include program code for controlling chambercomponents that are used to load the substrate onto a pedestal or chuckand to control the spacing between the substrate and other parts of thechamber such as a gas inlet and/or target. A process gas control programmay include code for controlling gas composition, flow rates, pulsetimes, and optionally for flowing gas into the chamber prior todeposition in order to stabilize the pressure in the chamber. A pressurecontrol program may include code for controlling the pressure in thechamber by regulating, e.g., a throttle valve in the exhaust system ofthe chamber. A heater control program may include code for controllingthe current to a heating unit that is used to heat the substrate.Alternatively, the heater control program may control delivery of a heattransfer gas such as helium to the wafer chuck.

Examples of chamber sensors that may be monitored during depositioninclude mass flow controllers, pressure sensors such as manometers, andthermocouples located in the pedestal or chuck. Appropriately programmedfeedback and control algorithms may be used with data from these sensorsto maintain desired process conditions.

The foregoing describes implementation of disclosed embodiments in asingle or multi-chamber semiconductor processing tool. The apparatus andprocess described herein may be used in conjunction with lithographicpatterning tools or processes, for example, for the fabrication ormanufacture of semiconductor devices, displays, LEDs, photovoltaicpanels, and the like. Typically, though not necessarily, suchtools/processes will be used or conducted together in a commonfabrication facility. Lithographic patterning of a film typicallyincludes some or all of the following steps, each step provided with anumber of possible tools: (1) application of photoresist on a workpiece,i.e., substrate, using a spin-on or spray-on tool; (2) curing ofphotoresist using a hot plate or furnace or UV curing tool; (3) exposingthe photoresist to visible or UV or x-ray light with a tool such as awafer stepper; (4) developing the resist so as to selectively removeresist and thereby pattern it using a tool such as a wet bench; (5)transferring the resist pattern into an underlying film or workpiece byusing a dry or plasma-assisted etching tool; and (6) removing the resistusing a tool such as an RF or microwave plasma resist stripper.

Experimental

Experiment 1

An experiment was conducted for four processes for depositing bulktungsten at 395° C. at a pressure of 40 Torr. In each process, bulktungsten was deposited on a tungsten nucleation layer deposited usingatomic layer deposition (ALD) alternating cycles of diborane (B₂H₆) andtungsten hexafluoride (WF₆). FIG. 14 provides example pulsing schemesfor each of these four processes. In Process 1, H₂ and WF₆ aresimultaneously and continuously flowed into the chamber, such as duringtraditional chemical vapor deposition (CVD). In Process 2, H₂ iscontinuously flowed while WF₆ is pulsed (e.g., pulsed CVD). In Process3, WF₆ is continuously flowed while H₂ is pulsed (e.g., pulsed CVD). InProcess 4, H₂ and WF₆ are alternately pulsed using a method such as thatdescribed above with respect to FIG. 4B (e.g., sequential CVD). Thethickness of the tungsten nucleation layer, the stress, nonuniformity,and resistivity of films deposited using each of these four processeswere measured and compiled in Table 1 below.

TABLE 1 Resistivity and Stress Nucleation Layer Thickness StressNonuniformity Resistivity Process (Å) (Mpa) (%) (μohm-cm) 1 507 225110.89 13.32 2 533 2207 4.31 12.79 3 517 2275 41.56 13.20 4 673 163421.77 10.81

As shown in Table 1, both the stress and the resistivity of the tungstenfilm deposited using Process 4 are significantly lower than the filmsdeposited using any of Processes 1-3.

Experiment 2

An experiment was conducted for processes for depositing bulk tungstenon two substrates, both substrates including a titanium nitride (TiN)barrier layer and a tungsten nucleation layer deposited by ALDalternating cycles of B₂H₆ and WF₆. One substrate involved deposition ofbulk tungsten using non-sequential CVD, involving exposing the substrateto WF₆ and H₂ simultaneously at 300° C. Another substrate involveddeposition of bulk tungsten using sequential CVD as described above withrespect to FIG. 4B, involving alternating pulses of WF₆ and H₂ at achamber pressure of 10 Torr. The fluorine concentration was measured forboth substrates. The conditions for this experiment are shown in Table2. The results are plotted in FIG. 15.

TABLE 2 Experiment 2 Conditions 1500 1501 Non-sequential CVD SequentialCVD Barrier Layer TiN TiN Nucleation Layer ALD ALD B₂H₆/WF₆ B₂H₆/WF₆ 10Torr Bulk Tungsten CVD Sequential CVD Layer WF₆ and H₂ WF₆/H₂ 300° C. 10Torr

Line 1500 shows the fluorine concentration for the substrate withtungsten deposited by non-sequential CVD. Line 1501 shows the fluorineconcentration for the substrate with tungsten deposited by sequentialCVD. The W/TiN interface line at about 350 Å represents the interfacebetween the tungsten nucleation layer and the TiN barrier layer. TheTiN/Oxide interface dotted line at about 475 Å represents the interfacebetween the TiN barrier layer and the oxide. Note that the fluorineconcentration on the y-axis of the plot is by orders of magnitude, andthe sequential CVD fluorine concentration 1501 is substantially lowerthan the non-sequential CVD fluorine concentration 1500—up to two ordersof magnitude lower in fluorine concentration at some substrate depths.

Experiment 3

An experiment was conducted for processes for depositing bulk tungstenon substrates at different pressures. Three substrates each included aTiN barrier layer. One substrate involved deposition of a tungstennucleation layer deposited by ALD alternating cycles of B₂H₆ and WF₆ at10 Torr followed by CVD of bulk tungsten by exposing the substrate toWF₆ and H₂ at 300° C. Another substrate involved deposition of atungsten nucleation layer deposited by ALD alternating cycles of B₂H₆and WF₆ at 10 Torr followed by sequential CVD of bulk tungsten byalternating pulses of WF₆ and H₂ at 10 Torr. A third substrate involvedALD of a tungsten nucleation layer deposited by alternating cycles ofB₂H₆ and WF₆ at 3 Torr followed by sequential CVD of bulk tungsten usingalternating pulses of WF₆ and H₂ at 10 Torr. The fluorine concentrationwas measured for all three substrates. The conditions for thisexperiment are shown in Table 3. The results are plotted in FIG. 16.

TABLE 3 Experiment 3 Conditions 1600 1601 1603 Non-sequential SequentialCVD Sequential CVD CVD at High P at Low P Barrier Layer TiN TiN TiNNucleation Layer ALD ALD ALD B₂H₆/WF₆ B₂H₆/WF₆ B₂H₆/WF₆ 10 Torr  3 TorrBulk Tungsten CVD Sequential CVD Sequential CVD Layer WF₆ and H₂ WF₆/H₂WF₆/H₂ 300° C. 10 Torr 10 Torr

Line 1600 represents the fluorine concentration for the first substratewhere bulk tungsten was deposited by non-sequential CVD. Dashed line1601 represents the fluorine concentration for the second substratewhere the nucleation layer was deposited at 10 Torr, followed by bulktungsten deposited by sequential CVD. Dotted line 1603 represents thefluorine concentration for the third substrate where the nucleationlayer was deposited at 3 Torr, followed by bulk tungsten deposited bysequential CVD. The results show that low pressure nucleation layerfollowed by sequential CVD (803) exhibited lower fluorine concentrationthan the second substrate (1601), even at the W/TiN interface and evenin the TiN layer (between 350 Å and 475 Å). This suggests there may bereduced fluorine diffusion into the TiN layer and the oxide due to thereduced amount of fluorine concentration in the tungsten film.

Experiment 4

An experiment was conducted for processes for depositing bulk tungstenon substrates using different combinations of tungsten deposition. Threesubstrates were compared. One substrate included 1 kA of thermal oxide,30 Å TiN, 18 Å tungsten nucleation layer deposited at 3 Torr using ALDalternating pulses of WF₆ and B₂H₆, and bulk tungsten deposited at 10Torr using sequential CVD pulses of WF₆ and H₂. The fluorineconcentration of this substrate is depicted by dashed line 912 in FIG.17. Another substrate included 1 kA of thermal oxide, 30 Å TiN, 10 Å offluorine-free tungsten, 12 Å tungsten nucleation layer deposited at 3Torr using ALD alternating pulses of WF₆ and B₂H₆, and bulk tungstendeposited by sequential CVD at 10 Torr using pulses of WF₆ and H₂. Thefluorine concentration of this second substrate is depicted by line 911in FIG. 17. A third substrate included 5 kA of TEOS-deposited oxide, 30Å of fluorine-free tungsten, 12 Å tungsten nucleation layer deposited at3 Torr using ALD alternating pulses of WF₆ and B₂H₆, and bulk tungstendeposited by sequential CVD at 10 Torr using WF₆ and H₂. The fluorineconcentration of this substrate is depicted by dotted line 1713 in FIG.9. The layers as deposited on each substrate for this experiment aresummarized in Table 4.

TABLE 4 Experiment 4 Conditions 1711 1712 1713 1st Layer 1 kÅ Thermal 1kÅ Thermal 5 kÅ TEOS- Oxide Oxide deposited Oxide 2nd Layer 30 Å TiN 30Å TiN 30 Å Fluorine- Free Tungsten 3rd Layer 10 Å Fluorine- 18 Å ALD 12Å ALD Free Tungsten Nucleation Layer Nucleation Layer B₂H₆/WF₆ B₂H₆/WF₆ 3 Torr  3 Torr 4th Layer 12 Å ALD Bulk W by Bulk W by Nucleation LayerSequential CVD Sequential CVD B₂H₆/WF₆ WF₆/H₂ WF₆/H₂  3 Torr 10 Torr 10Torr 5th Layer Bulk W by Sequential CVD WF₆/H₂ 10 Torr

As shown in FIG. 17, fluorine concentration for films deposited using acombination of fluorine-free tungsten, low pressure nucleation layer,and sequential CVD had less fluorine diffusion (see lines 1711 and lines1713 beyond the W/TiN interface where depths are greater than 425 Å).Fluorine concentration near the nucleation layer was lowest between 300Å and 425 Å for the film with more fluorine-free tungsten deposited onthe substrate, while bulk tungsten for the film deposited usingsequential CVD and low pressure nucleation without a fluorine-freetungsten layer had lower fluorine concentration between about 50 Å and300 Å (see line 1712). These results suggest that a combination ofdepositing fluorine-free tungsten and sequential CVD of tungsten mayresult in tungsten films achieving extremely low fluorine concentrationsand reduced fluorine diffusion.

Experiment 5

An experiment was conducted for processes films deposited by sequentialCVD in combination with low pressure versus high pressure nucleationlayer deposition. One substrate included a tungsten nucleation layerdeposited using ALD alternating cycles of WF₆ and B₂H₆ at 10 Torr withbulk tungsten deposition by sequential CVD in accordance with FIG. 4B asdescribed above using alternating pulses of WF₆ and H₂ at 10 Torr. Thestress and resistivity of the film was measured at various thicknessesand is shown as line 1801 “low pressure nucleation” in FIGS. 18A and18B. Another substrate included a tungsten nucleation layer depositedusing ALD alternating cycles of WF₆ and B₂H₆ at 40 Torr with bulktungsten deposition by sequential CVD in accordance with FIG. 4B asdescribed above using alternating pulses of WF₆ and H₂ at 10 Torr. Thestress and resistivity of the film was measured at various thicknessesand is shown as line 1802 “high pressure nucleation” in FIGS. 18A and18B. Conditions for the nucleation and bulk layer depositions are shownin Table 5.

TABLE 5 Experiment 5 Conditions 1801 Low Pressure 1802 High PressureNucleation Nucleation Nucleation Layer ALD ALD B₂H₆/WF₆ B₂H₆/WF₆ 10 Torr40 Torr Bulk Tungsten Sequential CVD Sequential CVD Layer WF₆/H₂ WF₆/H₂10 Torr 10 Torr Temperature 300° C.

As shown in the results, the substrate with the nucleation layerdeposited at low pressure had substantially lower stress than thesubstrate with the nucleation layer deposited at high pressure, whilethe resistivity remained approximately the same.

Experiment 6

An experiment was conducted for processes films deposited by sequentialCVD in combination with low temperature versus high temperaturenucleation layer deposition. One substrate included a tungstennucleation layer deposited using ALD alternating cycles of WF₆ and B₂H₆at 10 Torr and 250° C. with bulk tungsten deposition by sequential CVDin accordance with FIG. 4B as described above using alternating pulsesof WF₆ and H₂ at 10 Torr. The stress and resistivity of the film wasmeasured at various thicknesses and is shown as line 1902 “low Tnucleation” in FIGS. 19A and 19B. Another substrate included a tungstennucleation layer deposited using ALD alternating cycles of WF₆ and B₂H₆at 10 Torr and 300° C. with bulk tungsten deposition by sequential CVDin accordance with FIG. 4B as described above using alternating pulsesof WF₆ and H₂ at 10 Torr. The stress and resistivity of the film wasmeasured at various thicknesses and is shown as line 1904 “high Tnucleation” in FIGS. 19A and 19B. Conditions for the nucleation and bulklayer depositions are shown in Table 6.

TABLE 6 Experiment 6 Conditions 1902 Low Temp 1904 High Temp NucleationNucleation Nucleation Layer ALD ALD B₂H₆/WF₆ B₂H₆/WF₆ 10 Torr 10 Torr250° C. 300° C. Bulk Tungsten Sequential CVD Sequential CVD Layer WF₆/H₂WF₆/H₂ 10 Torr 10 Torr

As shown in the results, the substrate with the nucleation layerdeposited at low temperature had substantially lower stress than thesubstrate with the nucleation layer deposited at high temperature, whilethe resistivity of the film deposited at higher temperature was slightlylower than the resistivity of the film deposited at lower temperature.These results suggest that lower temperature deposition of thenucleation layer in combination with sequential CVD bulk deposition cansignificantly reduce the stress of the film.

Experiment 7

An experiment was conducted for bWL fill with and without nitrogenaddition. Nitrogen was added during hydrogen exposure for repetitions ofthe following cycle: tungsten-containing precursor exposure, purge usingargon, reducing agent hydrogen gas exposure, and purge using argon. Forthe substrate where no nitrogen was used, deposition was performed at430° C. involving deposition of a nucleation layer and repeateddeposition cycles for depositing tungsten as described above. Linebending analysis is performed by measuring the line width and roughnessof the trenches filled with metal (i.e. tungsten). The line bendinganalysis involves imaging the metal at the top of the device openingwith plan-view microscopy and measuring the metal width at multiplepoints on multiple lines. For each line, the line width is measuredacross 100 points. From each line, one then calculates the average linewidth and the variation of the line width, sometimes defined asroughness. The “Line width mean” is the average of all the individuallines' average line width measured during analysis. For line bending twomain metrics are defined as following: (i) line-to-line (LTL) variationis the standard deviation of the average line widths, thereby capturingthe variation of line width changes across different lines on the image(ii) line width roughness (LWR) is the average of line roughness(variation of line width within each line) from all the measured lines,thereby capturing the average line width variation within single lines.These two metrics, LTL and LWR are combined into single variationmetric, a total, as described above. Furthermore, LTL and σ total arenormalized with respect to line width mean, described as LTL % and σtotal %. Examples of these calculations are depicted in Table 7 below.

For the substrate where nitrogen gas flow was introduced during reducingagent hydrogen gas exposure where 50% of the flow rate was nitrogen gasflow, the deposition was performed at 435° C. A nucleation layer wasdeposited and cycles of tungsten-containing precursor, argon purge,hydrogen and nitrogen co-flow, and argon purge were performed. Theresulting line width mean, LTL, and LWR and the variance total, LTLpercentage and variance total percentage are depicted in Table 7 below.

TABLE 7 Experiment 7 Results Without N₂ With N₂ Deposition Temperature430° C. 435° C. Line width mean (nm) 19.74 21.11 LTL (nm) 2.68 1.15 LWR(nm) 1.11 0.97 σ total (nm) 2.90 1.51 LTL % 13.57 5.47 σ total % 14.707.13

These results are based on a cross section and top-down SEM imageanalysis. The pulse sequence used involved N₂ exposure during thereducing agent H₂ conversion. The results indicate that fill was goodand line bending was minimal, with 50% N₂ in the bulk process. Linebending in the substrate where N₂ was used was substantially less thanthe line bending found in the substrate where N₂ was not used.

CONCLUSION

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications may be practiced within the scope ofthe appended sample claims. It should be noted that there are manyalternative ways of implementing the processes, systems, and apparatusof the present embodiments. Accordingly, the present embodiments are tobe considered as illustrative and not restrictive, and the embodimentsare not to be limited to the details given herein.

What is claimed is:
 1. A method of filling features on a substrate toform lines, the method comprising: (a) providing a substrate having aplurality of features spaced apart with a pitch between adjacentfeatures of about 20 nm and about 40 nm, each feature having a featureopening width, wherein the width of the feature narrows from the top ofthe feature to the bottom of the feature; (b) depositing a first amountof tungsten in the plurality of features on the substrate; (c) afterdepositing the first amount of tungsten, exposing the first amount oftungsten in the plurality of features to nitrogen gas; and (d)depositing a second amount of tungsten over the first amount of tungstenin the plurality of features.
 2. The method of claim 1, wherein thenitrogen gas reduces tungsten-tungsten bonding interactions betweentungsten formed on sidewalls of each feature.
 3. The method of claim 1,wherein the width of the bottom of each feature is between 0 nm and 90%of the width at the top of the each feature.
 4. The method of claim 1,further comprising filling the features with tungsten to thereby formthe lines, wherein total variance of the lines within the substratecalculated by σ=(σ₁ ²+σ₂ ²)^(1/2) where σ₁ is variable line-to-linewidth variance and σ₂ is within-line width variance is less than about 5nm.
 5. The method of claim 1, wherein the width at the bottom 50% of thedepth of the feature is between 0 nm and 20 nm.
 6. The method of claim1, wherein the first amount of tungsten is exposed to the nitrogen gasat a substrate temperature less than about 500° C.
 7. The method ofclaim 1, wherein the first amount of tungsten is exposed to the nitrogengas during the depositing of the second amount of tungsten over thefirst amount of tungsten.
 8. The method of claim 1, wherein the secondamount of tungsten is deposited by alternating pulses of hydrogen and atungsten-containing precursor.
 9. The method of claim 8, wherein thefirst amount of tungsten is exposed to the nitrogen gas during the pulseof hydrogen.
 10. The method of claim 8, wherein the first amount oftungsten is exposed to the nitrogen gas during the pulse of thetungsten-containing precursor.
 11. The method of claim 8, wherein thefirst amount of tungsten is exposed to argon between the alternatingpulses of the hydrogen and the tungsten-containing precursor.
 12. Themethod of claim 11, wherein the first amount of tungsten is exposed tothe nitrogen when the feature is exposed to the argon between thealternating pulses of the hydrogen and the tungsten-containingprecursor.
 13. A method of filling features on a substrate to formlines, the method comprising: (a) providing a substrate having aplurality of features spaced apart with a pitch between adjacentfeatures of about 20 nm and about 40 nm, each feature having a featureopening wherein the width of the feature narrows from the top of thefeature to the bottom of the feature; (b) depositing a first amount of ametal in the plurality of features on the substrate; (c) afterdepositing the first amount of the metal, exposing the first amount ofthe metal in the plurality of features to an inhibition gas; and (d)depositing a second amount of the metal over the first amount of themetal in the plurality of features.
 14. The method of claim 13, whereinthe metal is selected from the group consisting of ruthenium,molybdenum, and cobalt.
 15. The method of claim 13, wherein theinhibition gas is selected from the group consisting of nitrogen,oxygen, ammonia, and combinations thereof.
 16. The method of claim 13,wherein the inhibition gas reduces metal-metal bonding interactionsbetween metal formed sidewalls of each feature.
 17. The method of claim13, wherein the width of the bottom of each feature is between 0 nm and90% of the width at the top of the each feature.
 18. The method of claim13, further comprising filling the features with the metal to therebyform the lines, wherein total variance of the lines within the substratecalculated by σ=(σ₁ ²+σ₂ ²)^(1/2) where σ₁ is variable line-to-linewidth variance and σ₂ is within-line width variance is less than about 5nm.
 19. The method of claim 13, wherein the width at the bottom 50% ofthe depth of the feature is between 0 nm and 20 nm.